my suggestion

1) You can try the safe mode as suggested.
2) the best way is using a XP boot disk and run
fixmbr and fixboot
3) see the following link as a final resort
get a PE boot disk and run the mbrwizard

http://www.mbrwizard.com/download.shtml
http://www.911cd.net/forums//index.php?showtopic=4261

ps do back up for any import data and read the instruction carefully because using the utility, it might destroy all data.

good luck