Hi Daniweb!

I'm going nuts here, this is my first IT problem I as a softwaredeveloper hasn't been able to solve myself... I'm just not that much hardware guy as I wanted to really be I guess.. :(
I have written a short synopsis of my problem, since my post got really long. You can read it first and decide if you are unable to help, as you don't have to read the rest then and use time on my post that is potentially thrown away for you, as it became quite long.

My computer has started about a month ago, to not been able to start on random occurences, which has been happening more frequently recently. When I turn it on, nothing appears on the screen, but it sounds like its booting, since I can hear it after some time reading from the DVD drive, as it does under boot. I suspect that it is in a reboot cycle though, as it after some time once again can be heard reading from the drive. I really doubt its a issue with the DVD drive, as it shows nothing on the screen, not even the POST screen.
I have been unable to reproduce the problem, it just happens on random occurences, and when it happens, it cannot be solved with a simple restart - It is persistent to some degree. I have tried restarting, turning it on/off, removing power cables, removing USB devices and generally just removing any non-neccessary peripherals. Nothing seems to be a certain solution for it, after having tried alot of restarts, and power cables removals and such random things, the picture just shows up on screen and it boots completely normal, and I can use my OS without problems for as long as I want. So in theory, my computer works, but sometimes I have this fights with it, where nothing just happens on the screen, but it does turn-on as in the DVD drive is making sounds, and the fans does power up. The fights with it seems to have been lasting longer and occuring more often, which is a bad sign.

I hope that gave some initial understanding of the problem. If you could understand it, and might know the problem, I don't hope my long post scares you away :-/ It is quite an odd problem, so I tried writing everything which I considered might be relevant for you, although it with the nature of the problem for me, is quite hard knowing whats relevant, sadly..

Deeper explanation:
My problem is quite odd. I built my system in 2007, and have NEVER had any problems with it before now.
What my system does is basically that sometimes when I boot it, the display never shows up. The fans in the cabinet spins up and their LEDs start glowing and I can hear the DVD drive trying to read a disc, just as it normally does under boot. Then after some time, it sounds as if it tries to read the DVD again, which makes me think that after a while, it reboots again(if it can reboot.. I don't know if it can be said that it booted in the first place).
No screen shows up at all, which means I'm not even met with the POST screen, so this happens before the OS is booted.
The major problem with this is, I cannot reproduce the problem, as it seems to happen just at random. It also seems to disappear at random, which makes it hard for me to find a solution.

Attempts at troubleshooting/finding the problem:
The first time it happened, I tried restarting my PC and turning it off and on to no prevail. After removing an USB NIC card from it and booting it, the screen then showed and I thought I had a faulty USB device and kept it out of my computer..
The second time happened some days after.. I tried restarting and turning it on/off which didn't work again. Removing all USB devices (and general unneeded cables such as the audio cable) except HID's didn't work as well... After powering my machine off by removing the power cable and putting it back in after 10-20 seconds, it powered on.
The third time that I tried to do anything about the issue was yesterday.. Yesterday neither removing or inserting USB devices and general non-vital cables, nor removing the power plug as I did last time helped. I just... Honestly rebooted it, restarted it, removed the power cable at random and all that, and suddenly after a restart the POST screen just came on.

More info about the problem and system:
The other odd issue about this thing is also, WHEN it then works and boots, it is running perfectly fine and with no problems. I can run graphically requiring applications/games with no problem on my machines and there are NO artifacts or freezes.

My own thoughts/opinion about the problem
This leads my to believe that the GFX isn't the problem as it isnt failing on me, during prolonged extensive GFX use. The same goes with the CPU, screen, sound, network.. None of them are failing on me a single time during a whole day when it finally has booted successfully.
I did anyway consider the GFX for some time, since I have replaced the stock cooling on it, with a passive cooling. I feared that although I did stresstest it heavily after changing the cooling to test its temperatures under idle and load was okay, it might have been placed wrong, so some of the chips that did not have a temperature sensor might have been damaged. It was a long time ago I replaced the cooling - about 2.5 years, and the problem has only started occuring during the last month, in which it though has begun occuring more frequently at a noteworthy pace it seems, sadly. It has been lagging a bit sometimes, in applications which I had not experienced before, but hard to say thats not software related.

Im considering the mobo, RAM or PSU are being the issue. I'm doubting the PSU, it should be capable of supporting the hardware (the hardware is listed at the end of my post) with enough wattage(650w), even though I know the capacitors in PSUs deteriorate over time.
The RAM is a hard one as well, I have experienced others having faulty RAM, and their computer did not want to start at all, until the stick had been removed. Mine does start (although it as mentioned might be rebooting), just without displaying anything on the screen, and sometimes it does start and when in the OS, the RAM works perfectly fine.
I fear its the motherboard, since I know its the most in focus during boot, and I am thinking that what that is failing in those prolonged sessions, might be a component of the motherboard, which is only used during boot, which explains why I can use my computer inside the OS a whole day easily, without any hardware issues.

All in all, I believe its either the GFX or the motherboard, and I'm inclining towards the motherboard as being the part that should be changed since its responsible for a big deal of the booting process. I'm just not sure at all, and it's a heavy price to pay for my stupidity, if it shows I was wrong and it was not the motherboard... Besides, IF i were to buy a new motherboard, it would be stupid to use money on an old motherboard with a socket that supports my now legacy CPU, it would be better to buy one for a new system, but that would require changing more than just the motherboard then... And that can hurt, when you are just a student, so I hope that I'm able to prolong the life of my system a few more years, till I can afford a new.

I would be more than really grateful, if anything could give their input, I am quite blank as neither me, nor any of my friends has experienced anything similar before :-/ Thanks a lot for your help :-)
Your help is more than just appreciated! I hope a hardware-man can help me out here :-) Or just a man wiser than me.

Hardware specs:
CPU: Intel Core2duo E8400 (never been overclocked)
PSU: Corsair TX650W
GFX: XFX 8800GT 512MB RAM (never been overclocked)
Mobo: Asus P5K-PRO
RAM: 4x 1GB Crucial DDR2 8500Mhz sticks (I know only 6400MHZ sticks was needed to support the FSB of the CPU in a 1:1 ratio. I bought 8500Mhz sticks in case I ever wanted to learn about overclocking a CPU and the technicalities of it and what happened, without having to then also overclock my RAM)
HDD: (1) Samsung Spinpoint 500GB 720RPM. (2) Western Digital 160GB 7200RPM
Cabinet: Antec ninehundred

Extra elements that consumes power in case its relevant:
1x PCI-E wireless NIC
4x~ USB Devices (1 USB wireless NIC(I need two wireless NICs, as my Unix OS doesn't recognize my PCI-E NIC), 2 HIDs, 1 Bluetooth d+ngle).
2x Audio Cables
2x Screens, one computer monitor, and one DVI connection to my TV.
1x DVD-RW/DVD+RW drive. Its from Samsung. i doubt its the problem, as it never gets to the boot process (I assume), since it does not display the POST screen. Besides its not first in boot priority, my HDDs are, so I cannot imagine its because of the drive. I cannot see more than its from Samsung without taking it out. If you want me to do that, just tell me and I'll gladly do it, I'm just grateful for your help.

Final notes/rambling, I hope might be able to help somehow:
I just ran some tests on my HDDs while writing this message, and they seem to be healthy, as all the SMART values on the disks seems to be ok.
I have for some odd reason NEVER been able to boot with my external USB harddisks connected to my computer, so I always boot my computer without the USB harddisks connected, and connects them when I am inside an OS, where they work just fine. One of the harddisks has an error, where it can read from it with full speed, but only write with about 4MB/s to it, but that is another story.. I assume the drive is dying as it gone above the warning threshold for reallocated sectors in its SMART diagnostics, so I rarely ever connect or use it anyway.
I'm also using the disks for dualbooting. On one disk I have windows 7, while I on the other have a unix-like OS. The Windows 7 OS is my primary OS which it boots into. I don't know if this matters at all. As said, it never gets to the OS selection screen (I assume), as it never shows the POST screen when it first boots when it has one of its buggy sessions, but I am not the hardware man :-/

Btw: I did not know whether to put this in the "Motherboards, CPUs and RAM" section or in the "Monitors, Displays and Videocards" section.

If it won't get to the POST display, then it is a hardware problem. If you can't remove the DVD drive directly, then the next time you get to a POST, go into the BIOS setup and see if you can disable it. Then see if the problem continues. That will at least eliminate the DVD/CD ROM drive as a cause. If that doesn't work, then there is some other hardware issue and you need to send it in for repair, or if it is more than 3 years old, replace it.

You're not going to believe this...

It's most likely the one thing that you haven't looked at. The first thing that I would do is replace the POWER SUPPLY UNIT, if yo uhave one lying around to swap it out with.

I have had 3 computers do the same thing to me... they were all partial swap-out builds, and after a good long time I realised they had a common thread... the PSU.

Funny, I just fixed a client computer the other day with the exact same issue, sometimes it was fine, sometimes not. swappd it out, and hey presto... HOPEFULLY it's an easy one for you to test and rectify.

But yes, it has to be a hardware issue. You could also do a little bit of looking around to see if there is a firmware update for the motherboard. thee might be an issue there, too.

Im having the same issue here, but my config is totally different from yours. But now my computer has another symtomp: by powering on by the motherboard switch, only the fans stir a little, then they stops, nothing happening. I have to disconnect then reconnect the power cable to get the same result. If I shortcut the PSU to power on, then it works, but not in the case when it is also plugged to the motherboard. I replaced the CMOS battery which was running low, but no effect. If it can be started, randomly gets to the POST, then works fine.

Update: my computer works better layed out on a piece of wood than in its box...
Sometimes the video card fails to boot (Showed by a red led that it is not used, and the BIOS beeps the absence of video card, but then not even the internal video card works)

Update: No reboot since last post, works fine. For now.
I think I found my hardware error: Bad capacitors around the CPU, some of them are deformed, needs cooling, but I have to replace them somewhen...

I replaced the visibly bad line of capacitors, it didn't solved the whole problem, but I was able to boot with a trick (?) :
While pressing the power button after powering the PSU, the video card's overheat red signal led stops for half a second, then I can release the button, and it BOOTS. (Cannot do this with only the internal vga, beacuse it is has no leds)
The final solution maybe replacing all of the bigger capacitors, but I will buy another motherboard. And CPU. And memory.

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