Hi, I have a computer from late 2007 with these specifications:
Windows Vista Home Premium
I'm not sure the model of my motherboard, but it is made by ECS
GeForce 8600 graphics card
Intel Core 2 Duo E6500 processor
2 GB DDR2 OCZ RAM
320 GB hard drive
Eagle Tech Cool Power 500 Watt PSU
For the past few weeks, My computer would reboot a lot and the time between reboots would vary between about 3 seconds and many hours. We looked up a bit why it was happening, and we found one guy's motherboard was dying, which I hope isn't happening to me, and another guy found his RAM and graphics card connections weren't in correctly. So we opened to computer and vacuumed a lot of dust out, but all the connections were good, although the problem still persisted. When the computer was rebooting like every 5 seconds, I would wiggle the PSU cable and the problem would be fixed for between a few hours and a day.
However, this afternoon, the computer wouldn't stay on for more than a few seconds before rebooting no matter what I did to the cable. After a while I realized something very bad had happened, because the little lights on my wireless keyboard signal thing weren't on (and they are still on when the computer is off). Also, I couldn't hear my PSU on (you can usually hear it pretty well when the computer is off). When I unplugged it and replugged it back in, the lights on my keyboard thing would go on for a second, but back off again. This all leads me to believe that it is the PSU. I got it for -1¢ (after only $20 in rebate) and the reviews weren't great. The only other thing could be the graphics card fan not running which I can't see even with my see-through case, but I think the computer would still at least turn on if it wasn't working. If you think it might not be the PSU, please tell me and thank you