How to Fix a Missing BOOTMGR
The latest versions of Windows, including Vista and 7, use the Windows Boot Manager to read the boot configuration files and data in order to load your Windows Desktop. If any of these files are corrupted or damaged, you will see a "BOOTMGR is missing" error. Fortunately, you can use a number of Windows tools to repair or replace the BOOTMGR or any related file that may be the cause of the problem.
Insert your Windows installation CD disk in your computer's CD drive and restart the computer.
Press "F8" repeatedly while the computer boots up. This command enters the "Advance boot options" screen.
Select the "Repair my computer" option and then press "Enter." The System Recovery Options screen opens.
Select the "Startup Repair" option at the top of the list and click "Next." The utility will scan your system for the cause of the BOOTMGR problem and repair it.