it’s often helpful to repair the MBR (Master Boot Record) to restore the Windows 7 boot loader—and you can do it easily from the Windows installation disc.
Repairing the Master Boot Record
If you want to restore the master boot record, you can simply type in the following command:
You can also write a new boot sector onto the system partition with this command (which is often more useful):
And of course, if you just use bootrec /? you’ll be able to see all the options.