During a gaming session, I was playing fine. The fans weren't very loud, it wasn't very hot, and then suddenly my computer just turned off. I don't know what's wrong. I believe it's a PSU failure, but when I plug it into my graphics card it lights up. What should I do, I just built it a week ago.
AMD FX 8150 Black Edition (stock cooler)
Gigabyte 990FXA-UD3 motherboard
ASUS nVidia GeForce GTX 660 DirectCU II 2GB GDDR5 (non-Ti)
Topower 500W PSU
8GB Patriot Viper Extreme DDR3 RAM (1866 MHz downclocked to 1333 by mobo)
1TB WD Caviar Green HDD
5 case fans (3 intake, 2 exhaust)
A PSU failure is entirely possible; Topower is not known for making great units. It is also possible a VRM on your mobo died. After being off for a while (and turn the switch on the PSU off too), will it turn on again? If not, will it turn on if you unplug the CPU power cable? Of course it won't POST, but if it turns on only when the CPU power cable is disconnected, the board may have popped a VRM. If it won't turn on even if the CPU power cable is unplugged, the PSU may have [partially] died. Any bad smells around the PSU grills?