I've got a client, with two machines (from different relatives) that are generically flaky. Both are branded OEM rigs (not the same), both are AMD AM2 DDR2 rigs though (IIRC). One of them, I tested for several hours, and I couldn't get it to fail. So I replaced the PSU just in case, and sent it on its way. This one got fairly hot during stress-testing, but swapping the Al block heatsink for a fancy four-heatpipe model didn't help, surprisingly. The second one, I did some stress-testing, and this one, temps skyrocketed, so I replaced the heatsink with a 4-heatpipe one, and temps were back under control. I figured that was the problem, so I returned it, as I couldn't get it to crash after swapping heatsinks, during stress-testing. I got reports after I returned it, that the machine was still "shutting off". I got the machine back in a few months later, along with its LCD monitor. I thought that I had found the problem, that it was the monitor's AC cable port, but it turned out that a brand-new cable I had pulled out of my stash to test with, turned out to be defective. I also got a few blue-screens, and finally pulled out 2x512MB of RAM and then it seemed more stable. I sent it back, with fresh cables for power for both the PC and monitor, and a brand-new VGA cable, in case it was the cables. Client said it was ok for a while, but then it started acting up again. I'm not really sure what to do at this point, as I may be getting both of these machines in to work on again soon. I fear that they may simply have motherboards that are getting old and need replacement. My current plan is this - to install a fresh HDD or SSD, perform a fresh OS install, and stress-test. If it fails the stress-test, then it would seem to be a hardware problem. If so, then try a fresh PSU. If it still fails, then it is most likely the mobo, no? Or possibly the RAM. I have another system I know works that takes DDR2 RAM, that I could drop the RAM into and test that way. If it does seem like the mobo, then I have some spare mobos too. But not exact OEM replacements.