after selecting repair>cmd prompt, enter:

BootRec.exe /fixmbr

you can also substitue the /fixmbr with thes commands:

/FixBoot. Writes a boot sector onto the system partition to start Windows

/ScanOs. Scans all disks for Windows installations and displays them to you.

/RebuildBcd. Scans all disks for Windows installations and prompts you to pick the ones you want to add to the BCD.

Procedure for Windows 7 :

BootRec.exe /fixmbr

BootRec.exe /fixmbr

BootRec.exe /FixBoot

BootRec.exe /ScanOs

BootRec.exe /RebuildBcd