edit: Also heard that sometimes in Skyrim his screen randomly gets cut in half onto opposite sides. O_o
But when he plays BF3 (most demanding game) He gets nothing at all. No BSOD's or anything.
This is basically what I'd recommend first. I don't run Intel, but WoW was incredibly picky about overclocking on my last machine, whereas other programs were not.
The following site will give you more information on the Ox124 STOP error, which is what is causing the issue. As others have said, it is likely due to the OC'd. It could just be that the computer can't handle the OC anymore. If your friend is going to OC, then run Prime95 and let that stress test the pc. If the pc crashes, then your pc will not handle the OC. That is the best way to find a stable OC.