If you use a PC with multiple HDDs, you might forget to set the correct boot drive when doing a fresh Windows 7 install. This results in the fact that Windows creates the bootmgr file and boot directory on another drive. If you swap this drive afterwards, Windows will not be able to boot.
As described here, you only need to do the following steps:
- Copy boot directory and bootmgr file to your Windows system drive; ignore warnings.
- Run bcdedit /export C:bootbcd (if C is your Windows drive)
If it doesn’t work, you maybe have to set the Windows partition as active via diskpart.
If everythin runs fine, you can delete the old boot files.