you could try looking in the event viewer and or any minidump files to diagnose the problem but its sounding like you best bet is going to be the repair install.
Word of caution, if you repair to an earlier service pack you may experiance problems. I remember once I did a repair install over SP1 and it broke RAS, some registry editing was required to get any internet connection.
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"