Hey there,
I'm running a system that was built for me but I am not completely familiar with the specs. Its about 2 and half years old. Its a WinXP, 200gb, Asus Mobo, AMD Athlon, 2gbRAM, 400W PSU system as far as I know.

Maybe a month ago, the computer started to just switch off on me for no apparent reason. At first I ignored this thinking it was because I was overworking it. Of course, as this happened I did all the usual virus checks but came back clear. (I have witnessed the BlueScreenOfDeath three times throughout this process but it has run again perfectly after appearing.) Also before it went completely kaput this evening, it restarted twice on its own.

Then it started to not boot up correctly...
When I press the power switch, both the PSU and the processor fans initiate and run fine. The hard drive sounds as if its spinning and the CD-Rom drive is useable however nothing appears on the screen. After a couple of times of pressing the on switch on and off, it does the single beep as it did when it worked normally and continues to boot as normal and works fine. Until today, where it has not progressed after switching on and off. The light on the front comes on and the fans are running but nothing is sent to the monitor and the beep is not present. (Twice to start with it loaded to the POST screen but froze at AMD Athlon) but since has not got to even switching the monitor on.

So far I have tried removing all USBs and peripherals from the back of the unit. I have also tried removing the hard drive and the cd-rom to see if I could isolate a problem. Remember that it was running fine for at least 6hrs today doing the usual tasks. I have not made any hardware upgrades since the PSU upgrade about a year ago.

Any help would be much appreciated. I was thinking maybe that it could be the power supply failing to get enough power to the HDD or something, but I don't know enough about this.
Thanks

One of thiese components could be the cause:

- PSU - no way to tell unless you have spare one to test

- Motherboard - same as above

- CPU - same as above

- Memory - running on one stick at the time to see which one is faulty. Removing all would invoke booting with video feedback, but with POST error + beeping

- VGA - unless it is on-board, removing it would invoke POST error in a way of beeping. Also reseating it can resolve the problem.

You could test the power supply in a different machine to see if it works correctly in it, and that might help. Sounds kind of power related.

take out some other components and reseat them/test the computer without them present (the video card, the memory) and see what how it reacts.

I tried the PSU in another computer and had the same issue where the lights came on but it didnt reach POST. Then I figured that I should buy a new PSU which I did and am having the same problems on BOTH computers now. Now I have put the original PSU into my second (working) computer and it wont start even though it had been working this morning... So I have two dead computers. Really starting to flip out now. The second computer showed no signs of trouble.

maybe the psu is damaging components somehow. If you have a voltmeter, perhaps you should check the voltage of the main power and perhaps some of the peripheral connectors to see if there's any problem with the voltage (maybe it's overvolting and blowing something up) that could explain the problem you had with your test computer.

Maybe you haven't properly plugged the working PSU in recently working PC back?
Also, the power connector solders could've got cracked while plugging in and out. Not uncommon. Check them from the other side of the motherboard. You might need magnifying glass.
And, unless you know the nominal volt values, there is no use of measuring the voltage output, unless you have some really high volts running through. Thing is, voltages are so low that conventional voltmeters wouldn't show them correctly at all. They might seem accurate, with all those decimal values, but the reality is they are very inaccurate. You would need pro equipment to get clear readings.