This machine did have a failing PSU, which I have replaced. (12v rail powering up to 13.7v intermittent), and did cause the video card to burn out, (also replaced). The computer will now run fine for a long time, (anywhere between 8hrs and 16hrs before powering off). I have vacuumed out the interior of the computer, and cleaned the CPU fan and heatsink. However, the computer will randomly power off after running for between 8 and 16 hours. During the time the system is up, it runs perfectly fine. When power is lost, it is just as a power failure has happened and/or the cord was pulled from the back of the machine. In order to power the machine back up, the power cable must be removed, the PSU shut off, the power cable re-inserted, and the PSU turned back on before turning on the machine. After the machine comes back online, it operates fine until the next power failure. What else would be causing this problem? Failing CPU? The only stupid question is the one not asked.

Using a vacuum on a computer is a sure way to damage sensitive components. Electrostatic discharge can and may have damaged something. Did you replace the PSU with a comparable unit? Your problem sounds like a power supply issue. What are all the specs and what is the model of the replacement PSU?

The previous PSU was an Antec SL400, and the replacement PSU is an Antec SL550. No, I did not use a regular floor vacuum to clean the interior of the computer, but a "keyboard" vacuum. I was grounded to the machine when I did the vacuuming out of the machine. The only stupid question is the one not asked.

I think I found the problem. The HSF was full of dust, and causing the idle temperature to be at 58C. I've since cleaned it, and now I need to go buy thermal paste to reattach the HS. The only stupid question is the one not asked.

Odd that overheating would take that long. You must have been triggering the overheating by stressing the the CPU.

Well, after cleaning the HS, and attaching a secondary fan to the HS, (and adding a case fan), the computer has been running non-stop since 29 Sept. The computer has not crashed, and is stability running at 41c. Under load, it gets up to 51c, but I consider that acceptable. The only stupid question is the one not asked.