My computer will have varying stretches of time where it will shut itself off randomly. Sometimes it's constant, before the computer can even boot. I know it's not overheating(been gauging the temperatures). When it shuts off, if I leave it without hitting the power switch or unplugging the cord, it will sometimes turn itself on again for about 5-10 seconds and then shut itself off again. It sometimes would do this repeatedly. Other times after shutting itself off and if I don't hit the power switch or unplug it, it won't turn on until I hit the switch/unplug and (I'm guessing?) let the excess power dissipate before it can be turned on again, usually just so it can start all over. I've run full system scans with different programs and gotten the green light on everything hardware related, and have tried formatting.
Other times it runs perfectly fine without issue.
AMD Athlon II X3 455 CPU
8GB Wintec DDR3 RAM
MSI N1966 Mobo
AMD Radeon 6950 1GB
Corsair CX500 500w PSU
Windows 7 SP1
Any help would be greatly appreciated.
EDIT: I forgot to mention that I've already had the PSU replaced once, thinking that was the issue. So yeah, apparently that is not it.
N1966 is apparently not the model number of the mobo itself. The simple fact that it's a MSI AMD board though makes me suspect it has simply croaked. Look it over carefully for leaking or bulging capacitors. Google is very friendly, and will show you lots of images if you search for "bad capacitors." If you find any, you may be able to replace them (if you have some desoldering/soldering skills and tools). Otherwise, you'll need to get a new motherboard (which probably means a new Windows license as well).