Bah, using my name in vain again are you? Yeah, sounds like an overheating problem. Not as a permanent solution, but as a test, you might want to underclock the CPU/ram in the bios. If it no longer crashes, you atleast know what the problem was. In a pre-built laptop they usually make sure there are no hardware conflicts, so I wouldn't think it would be the graphics card (unless it's busted or something). Anyway, sounds like overheating. You could also run one of those cpu cooker tests and see if it restarts then. That would test for system instability in overheating without using the graphics adapter in the same way. Hope it gets better. Oops, just read the above message about the heat sink... Well... uh. Looks like that mystery is solved!