You can try to Repair your Windows using the Windows installation CD (for Repair choose R when prompted). You can let the automatic repair to try and fix it, if that doesn't work upon restart reboot and start the Repair again, but this time select Command Prompt or Console and put in "bootrec /rebuildbcd" without the quotes. If you don't have Windows installation CD you can try downloading Hiren's Boot CD and try to fix the bootmgr with the utilities from the disc: http://www.hirensbootcd.org/download/