I sometimes get this popup in the System Tray that says "Your computer has multiple security problems" (Or that that likeness) and then the whole computer crashes and shuts down. So far this only happens when I am doing some online gaming. I think it could be some overheating but IDK if that security message has anything to do with that. So any ideas? My computer is a Vista x64 SP2.

Update your Antivirus and make a full scan Download and make a full updated scan with malwarebytes. I think that you may have a problem with malware. Your symptoms do not sound like overheating.Adware Removal