XP MasterBoot ok, but machine auto-restarts

I deleted the linux ubuntu partition from windows. Found that after restarting machine, the GRUB was missing. I fix the master boot record problem using ‘fixmbr’ command from WINXP set up and then ‘repair’ the windows. but now the problem is grub is loading, but after that the computer automatically restarts. So its a process of continuous restarts. I hope i conveyed my problem properly. Someone please suggest how can i recover from this. At worst i have to install a fresh copy of windows, which as u understand i dont want.

So, please i help. I think this problem is pretty common, there must be a solution.