Need professional help, why does my computer keep rebooting?

When using the on-board graphics my computer is fine, when using a PCI-E graphics card, my computer seems to freeze and reboot at random. But it's rebooted once or twice using on-board. I've figured out what it isn't:


-Not the PSU (used 5 diff ones)


-Not the graphics card (tried with 2 different ones)


-Not overheating, CPU idles at 35-40*c, system temp 20-30*c, GPU 55-65*c, like always.





It could either be the CPU, motherboard, RAM, or a driver issue most likely, but I've tried with a couple of different drivers too.





Here's my hardware setup:


CPU: AMD Sempron 3300+ (socket 754)


Motherboard: GYGABYTE GA-K8N51GMF


RAM: 2x DDR400 512MB (1GB total)


GPU: XFX NVIDIA GeForce 7900 GS (also tried with a GALAXY NVIDIA GeForce 7600 GS Premium with same problem)





I usually know what I'm doing when dealing with problems like this but I've tried everything (except testing with another motherboard/CPU) and I'm really lost. I could do with help from someone who really knows their stuff, thanks.

Need professional help, why does my computer keep rebooting?
That exact motherboard is all over forums for the same issue. It is most likely your culprit. It could be a single bad capacitor. Replace it.
Reply:try removing one of your RAM.. (the second in line), then see what happen... this kind of problem is from memory card sometimes.
Reply:uh did u install the driver o_O?
Reply:I had a rebooting problem, It was caused by, of all things, my dvd burner, every time I'd put in a cd, It crashed. Also, if it had any cd in it on startup, windows would never get to the xp red and black startup screen. It would crash over and over again. Now I took out the burner and all is fine. Weird!
Reply:have you gone into device manager to check all the drivers also mite be a virus but I doubt it
Reply:I have seen this issue many times before. Check the capacitors if they are not flat on the top you have a mother board issue and the first step is to replace it. You won't know till then if your CPU, RAM or video card is OK because overloaded capacitors can destroy any card or chip plugged into the board. The most likely cause of this issue is power fluctuation on the circuit your computer is operating on. Buy a UPS with line conditioning and that should prevent the issue in the future. Also it is possible to have this problem with a good PSU.