Games Keep Crashing

My friend has a custom built gaming PC and recently he has experienced game crashes quite frequently. All Steam games crash, as well as all Blizzard games (Unexpected Fatal Error). He has updated video card drivers, but to no avail. I know he replaced the GPU as well as CPU. Perhaps he did not do it right, or could this be a power issue? His dad built the computer and replaced the parts, so he doesn't know about his Power Supply Wattage.
Thanks in advance.

Here is his build.
Specs
CPU: AMD Phenon 2 X4 970
Memory:Corsair 8 GB
GPU: GTX 670
MOBO: ASRock M3A770DE