Disconnect non-essential hardware, run a memory test click here, does the FSB/memory speed also affect the shutdown problem? Max temp for those chips is about 85C but I wouldn't let it get near that if I were you, not that you have much choice at the moment. Mine used to hover around 50-60C, the latter only under extreme load. If you feel competent, pull it apart and reseat the processor with some high quality compound. Take out and refit the memory chips too.