http://www.computerforum.com/15602-bootmgr-missing- help.html

Try the repair option of the Windows XP OS. You do this by booting from the CD. Wait till you get the welcome screen and then press R. Then type in CHKDSK /P and then CHKDSK /F. Then, after this is done, type in FIXBOOT and after that is complete, type in EXIT. This could fix your problem.