Computer shuts down randomly, takes a couple hours to turn back on (not due to heat)

Okay, so this is not a unique problem. At least a first blush. I've been reading these forums for years, along with others, and consider myself somewhat computer savy. That being said, here's my seemingly unsolveable dilema:

I built my computer a couple years back. Here are my specs:

WD Rapter 74GB Serial ATA HD
MS Windows XP Pro OEM version (newest service pack)
Pentium 4 3.6Ghz 660
Intel D945PSN Board (newest BIOS)
Xfinity 500 Watt ATX power supply
1 DDR2 @ 1GB
1 DDR2 @512MB
Nvidia 7800GT

Everything ran fine for about 6-8 months, then after moving my computer would sometimes power down at random. After doing a lot of research I discovered it was due to overheating (typical in these situations). I applied new thermal grease, and everything would appear fine for awhile. Typically, I would find my computer turned off overnight, or while playing a graphics intense game. This was ultimately due to overheating. I inspected the board, there are no ruptured/eroded capacitors, and no shorts/contacts interfering with the board and the case. I ultimately discovered that the CPU fan (stock) for the P4 did not have copper connections and was entirely aluminum, keeping my processor at 55C idle and ~68-71 full load. After 15 minutes it would shut off, which is expected. However, it doesn't turn back on for several hours, and usually the I/O has to be off during this time (capacitor draining?, some other reason?).

Today I bought the Cooler Master Hyper TX 2 and (after many cuts) installed it. I ended up removing the motherboard to ensure proper fit. Upon restarting the idle temperature was ~49C and at max ~61-65. This would suggest that everything was solved, but once again the problem re-emerged: Once the computer turned off the monitor the computer shut off again. I'm confident it can't be an overheating issue, as it never tripped the sensor above 70C. I'm thinking either the motherboard has a problem with coming out of power saving mode, or something else that I can't imagine. When the computer is off, I cannot turn it back on without unplugging/turning off the I/O. Even then I must wait a least a couple hours before it will restart (long after all systems are cool).

If anyone has any idea what is going on I would love to know, my endless research has yielded nothing beyond capacitor defects, overheating, defective ram (which by the way do not solve the problem when removed), etc. Sorry for the length of this, but I am at wit's end.

 

Re: Computer shuts down randomly, takes a couple hours to turn back on (not due to he

Oh yes, one more point:

When I do switch off the PSU and turn it back on (after the lights on the motherboard turn off) it flashes on for about 1 second and the fans all turn and then it immediately turns off. This happens no matter what is attached/removed from the motherboard. Only after a cool down period (usually well over an hour) does everything boot up fine again, and run normally until deciding to shut off. This can happen after an hour, or after several days use of turning on and off.

 

Re: Computer shuts down randomly, takes a couple hours to turn back on (not due to he

Update: Computer turned back on, was running at around 44C-50C as I did some diagnostic checks...turned off during the checks, but the temperature did not go above a normal level (using Intel's Active Monitor). Still no idea why this is happening.

 

Re: Computer shuts down randomly, takes a couple hours to turn back on (not due to he

Sounds like possible hard drive failure. While the computer itself may not be failing, the Hard Drive may do so, and it looks identical to a complete failure. When it next happens, shut the computer down with the PSU switch. Wait a short time then try starting it. If it brings up the bios then fails, that's the clue. Try getting into BIOS and checking for the HD then. If the HD is still warm, but the rest is cool, it should not detect the HD.

 

Re: Computer shuts down randomly, takes a couple hours to turn back on (not due to he

Thanks for the reply. Once the computer fails when I restart it does not bring up the bios. Instead it flashes the front hard drive light/spins all fans on the computer for a very short time (half a second maybe) then immediately turns off. The power LED as well as the boad/networking lights remain on, but the computer will not power back on without switching off the PSU. Even then it's the same half second flash unless I wait for a least a couple hours. Then it powers back on like nothing is wrong. If it was the hard drive I'd expect it to just not detect it, but once it allows the system to POST it detects everything with no problems. CPU is now ~42C idle, Zone 1 38C Zone 2 32C.