Computer Keeps resarting

Hello,
Okay so the other night i installed the newest update for my computer(XP Home SP2) but i turned off my comp. before it could restart. Now when i turn it on it goes to the mode selection screen. Now if i select any of the safe modes it freezes once it loads something ending in MUP. If i try to start from the last good configuration it just resarts. If i try to start windows normally the screen will flash white for a split second then it resarts. I've tried the whole system repair with the disk, it just tells me that it cannot detect my drive. Is there anything i can do that wouldn't result in losing everything? PLEASE HELP!!!!!!!