You need to do a windows repair. Boot with your CDrom XP do a repair. It will reinstall windows and retain your current settings. you will have to do hardware driver re-intalls so make sure you have all your hardware drivers ready.
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EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.