- Start your pc in with CD-ROM support and windows installation cd on it.
- When prompted, press R to repair a Windows XP installation.
- If you repairing multiple operating systems, select the appropriate one (XP) from the menu. If you have only one operating system, enter 1 to select it.
- Enter the administrator password if prompted
- To fix the MBR, use the following command
- Type y and ENTER to fix the MBR
- Type exit and press enter to leave the recovery console and reboot system.
for additional info
to install recovery console in windows xp read this post