Maximum PC

Four days ago I was on my computer (its a dyi - about mobo, hsf, and psu about 5 years old, other components are newer) when it suddenly shut down. I then pushed the power button and nothing happened. I unplugged it, tried to turn it on and again nothing happened. I then tried a third time and it booted up fine. CPUID show temps are all fine.

It's never done this before, and so far if hasn't done it again.

Any ideas why it happened?

It could be PSU-related. Check the voltages on the 3.3v, 5v, and +12v rails and ensure that they are within acceptable (usually +5%) ranges.

If it seems slower than normal or the fan(s) were running at full speed the CPU could have overheated. But otherwise I agree the PSU is the likely culprit---though if the PSU detects certain conditions like undercurrent it will shut down to prevent damage.

If it is plugged into a UPS that would rule out some issues. The fact that it started up later when it may have cooled down or electric current quality was restored.

I would open it up outside and clean it out really good with canned compressed "air," especially around the CPU fins. Being 5 years old replacing the thermal paste would not be a bad idea. Inspect the board and other components for problems like leaking caps.

But being 5 years old the PSU may have just signaled it is on its way out.

Other than inspection and cleanup I would not replace anything unless it occurs again.

It's plugged into a UPS. So far, it hasn't happened again.

A few weeks ago it started again. Now it will stay on for about two hours, then shut down. Yesterday my burner stopped working, though Plex Utilities can find it. Today my DisplayPort connection stopped, and I had to connect the graphics card with the DVI connection. Temps seem fine. I don't know if it is the PSU, the mobo, or something else. Any thoughts?

The most likely culprit is your PSU. I would recommend changing it. Once you have that issue rectified, any other problems should be easily resolved.

My personal experience has been that the PSU is THE most likely component to fail in a computer, especially if the computer has worked well in the past.

The good news is you're at a good time to evaluate if you want to build a completely new system (you mention several parts are 5 years old), or if you just want to replace the PSU. Either way, buy a PSU from a reputable manufacturer. Corsair and Seasonic are highly respected. I've also had good luck with OCZ (they also own PC Power & Cooling, another respected brand).

Hope this helps.

Actually, i'm getting ready (in a couple of weeks) to do a new build. I'm hoping to use the burner and the displayport connection in the new build - is there anyway to tell if the psu has done any permanent damage to any of the parts before I install them in the new build?

Other than a spot check to see if something burnt out, no.

It would also depend on what make and model of PSU you have in the system currently. If it is a high-quality PSU from a reputable manufacturer, it should have active PFC and over-voltage protection built in to it. If it does, and the voltages are tightly regulated, there is a good chance that the damage to your other components in the system is minimal or (possibly) nonexistent.

Antec Neo 500.

Ok, after I pulled out the harddrive without the OS and pulled out the soundcard, the computer is fine. It's been running for 36 hours straight without any issues. What gives?

Antec NeoHE 500, from late 2006.