Did I screw something up or what?

I need help. Before I spin my tale, let me post my specs:

ASUS M4A78LT-M LE mobo
AMD Athlon II Quad-Core 640 Processor 3.00 GHz
EVGA GTX 560 TI Superclocked GPU
Kingston HyperX Blue DDR3 RAM 8GB
Corsair TX650 Enthusiast PSU
Thermaltake Case, Liquid Cooled
Windows 7 Premium Edition
Microsoft Security Essentials.

I have had my gaming rig for a couple of years, and I decided to perform an upgrade to make my general gaming experience better. The currently installed equipment replaced an Radeon HD5450 GPU, a stock 450W PSU, and 4GB of Crucial RAM. The install went relatively well and I fired up my machine and let it run for several hours when my problem started. The problem that I have is that at random intervals, the motherboard seems to shut down. It doesn't kill power to the case fans or to the liquid cooling pump that is powered by the cpu fan connector, and it doesn't cut power to the DVD-ROM. The motherboard power light stays on, but the GPU and all peripherals connected to the USB ports, as well as the HDD, shuts off. When I was wiring everything up I had to remove the radiator and fan for the liquid cooling system, and as I was going back over what I had done I discovered that for several hours after my upgrade the system had been running with the radiator cooling fan installed backwards.   I re-installed the fan (correctly this time, checked the arrow and everything) but the problem continues. Did I manage to fry my CPU by reversing the fan? Would that cause this problem? Or is the motherboard suspect?