Insert Windows Vista Installation CD/DVD, and boot from it.
Select language and keyboard or input method, click Next and choose to Repair your computer.
Then you will need to select the operating system that you want to repair.
In the Systems Recovery Options dialog box click Command Prompt, and type the following:
If you want to completely rebuild Windows Vista Boot Configuration Data,
then you should issue the following command:
This command scans all disks for installations that are compatible with
Windows Vista. Additionally, this option also allows select the
installations that you want to add to the Boot Configuration Data store.