A common problem on Windows Vista and Windows 7 computers is the "BOOTMGR" error. It appears as soon as Windows starts to load and might say "BOOTMGR is missing" or "Couldn't find BOOTMGR"... either way, it's the same issue.
There are several things you can do, however. A startup repair is the obvious fix but that doesn't always do the trick.
This how to guide should help you fix BOOTMGR errors
in no time.