Try stripping your system down to PSU,Motherboard,one stick of ram, and video (unless your motherboard suports integrated video) and add one part at a time untill it fails. The part that causes failure is the problem. If it fails right away then your motherboard is the most likely culprite.

A bad motherboard could have also caused the overheating problems.If your system fails you'll need to replace the motherboard and hope it didn't fry anything else.