All the lights go out on mine when it overheats, and then there's a puff of white smoke.

That's a brilliant idea, but why does your PC have cooling issues? I literally never worry about overheating because I sized my radiators and heatsinks adequately for my equipment, fans set in a positive pressure configuration to minimize dust accumulation. All I gotta do is clean the filters once every few months, and everything stays cool and clean.

If your overheating issues are a result of budgeting issues, I feel for you. Otherwise it wouldn't be a bad idea to invest in better cooling so that you never have to worry about temps.