Crashing & Hard Reset Needed

Hello everyone,

I've been having this problem with my computer since I had it built a while back. When I'm doing anything on my computer it will sometimes completely freeze up and I will have to do a hard reset to fix it. After I do a hard reset my mouse and wireless network adapter (It's a USB one) will have to be replugged for them to work again.

I've tried getting a new HDD and graphics card, both of those replacements failed in remedying the problem. I'm completely unsure of what could be causing the problem now.

I'm not sure if this is related or not but I originally had another motherboard of the same type in it but it failed, then later I had to remove one RAM stick (I originally had 32GB of RAM in the computer), but now I've had to remove all of the sticks except the one. Also, Speccy shows that my RAM is at 670MHz while I have it set to 1600MHz in the BIOS.

Here's my specs:
Operating System: Microsoft Windows 7 Professional 64-bit SP1
CPU: Intel Core i7 3930K @ 3.20GHz
RAM: 8.00 GB Single-Channel DDR3
Motherboard: ASRock X79 Extreme4
Graphics: AMD Radeon HD 7900 Series
HDD: 1024GB Western Digital

Any help would be really appreciated; thanks so much in advance.