personally I would do what Fastgame said with the sfc command. and if I can add to his post you will need your xp cd in the drive to run the command. it basically in a nutshell replaces any corrupt system files with good ones off the cd. if this works just make sure to rerun your servicepack1. then if that does not work do as FG said and to a xp repair, making sure and try to back up your personal data for safety.