Originally Posted by fireplace_tea
These things are so hard to troubleshoot without being there in person. It could be that you really do have a hardware issue. Is the computer over heating? Is there a lot of dust around the fan or CPU? Is everything still cleaning plugged in on the motherboard? A clean install typically formats the drive first, so it shouldn't be a software issue.
This could very much be the case. From the specs you gave it sounds like the machine should perform fairly well. Dust around the fan or CPU could cause it to overheat. I'd try to adjust a few settings first to see if it helps, but if that doesn't work then open it up and check the cleanliness.