Hey, i'v had my comp for a few months now, the problem only started recently, but i can't figure out whats going wrong. Sometimes when it turns itself on the computer seems to start up but the lights on the keyboard don't flash and the monitor doesn't display anything, when turned off and on again it usually starts up fine.
These are the specs:

CPU - AMD Athlon 64, 2200 MHz (11 x 200) 3200+
Motherboard - Asus K8N-E Deluxe (5 PCI, 1 AGP, 3 DDR DIMM, Audio, Gigabit LAN, IEEE-1394)
Motherboard Chipset - nVIDIA nForce3 250Gb, AMD Hammer
System Memory - 1024 MB (PC3200 DDR SDRAM)
BIOS Type - AMI (10/04/04)
Video Adapter - RADEON 9200 PRO Family (Microsoft Corporation) (256 MB)
Audio Adapter - nVIDIA MCP2-S - Audio Codec Interface
Disk Drive - Maxtor 6B200P0 (200 GB, 7200 RPM, Ultra-ATA/133)
Optical Drive - LITE-ON DVDRW SOHW-1693S

I just copied and pasted what i thought could be relevent from another program, from what i can tell the temperatures for the hard disk, the cpu and the motherboard are well within normal at 32°C, 36°C and 27°C respectively. Not too sure about the power, but it seems to be where the manufacturers say it should be.

All the fans are running normally as far as i can tell, the prgram i'm using (Everest Home Edition) tells me the fan that it can detect is running as roughly 5720 RPM, there are also two other fans on the computer, a side fan (which doesn't seem all that powerful) and what i'm guessing is the cpu fan, the hard disk doesn't appear to have one. There also don't appear to be any odd noises coming from within the computer.

There doesn't appear to be much consistency with when it does it either, it can do it about 4 times in a day or not do it at all, i've ran
powermax on it and all the system tests have said that the hard disk is fine, the cpu seems to be running normally as well, and the problem actually seems less prevelent when i'm playing games such as max payne 2 or halo. I've also tried reinstalling windows and nothing appears to happen. Needs cleaning perhaps?

Anyone think they can help?

Also bear in mind that i don't actually know all the much about poking about inside PCs.

Are you getting any error messages when it happens? It could be a problem with system RAM or a video card not completely seated. Check all the RAM, cards and cables to make sure they are seated and then try the system again. You may want to download and run memtest86 (Gogle for it). If you are still having the problem see if you receive any error messages or try to determine if it happens only when running specific problems. BTW, did you add any new hardware, update any drivers, or install any new programs around the time the problem first appeared?

hey, i think i've figured out wot it was, i opened up the machine and discovered that the PSU power box thing was loose, looked round the back at the screws and discovered that they weren't fixed in properly and had been forced in, the guy that built it used wood screws to secure the PSU into place, which i think was causing the whole thing to wobble when it was on, i think this was wots been causing me problems anyway, it appears to have gone away since i replaced the screws with the standard type that are supposed to go into it. i'll post again if the problem keeps occuring.
Does anyone think that this is a particually likely explanation for why it was doing this, give that the screws in it were about 3 times longer than they should have been.
thanks for the help BuggZ, and no error messages or recently installed hardware, numerous software installs though

My friend and I both built PC's, and, at one time or another, both either shut down randomly or wouldn't start at all.

Either way... my problem with my box was that my heatsink was shorting the board-power wasn't going to the right places. My friend had a fried pin off the motherboard power cable (20-pin). Either way, these bootup troubles occur when power isn't traveling. RAM has been found to act similarly.

the probs persisted so i opened it up to check the pins like BeastOverlordH6 said and discovered that the mother board also was not correctly fixed. it only had two screws holding it on, after the mother board was fitted with the rest of the screw i checked the pins and found no problems, but since everything has been fixed properly into place i haven't been having any problems with the comp.
just wanted to say thanks for all the help
c ya

Happy computing, dood.