Something is overheating, or your video card is dying.,,, Also make shure your BIOS is to default and dont OC the video card. Leave the side door open on the case, and put a house fan to it.
If it happens again then its not overheating. Its something else. Probably messed up video drivers or something....,,
Try using another hard drive...... if anything else is fine...... it maybe... OLD =P
[ mine died in a ..... very VERY wrong way =S ]