Restoring the Windows 7 boot loader may become necessary on rare occasions. Below is some ways that may save you from doing a complete re-install.
Use Windows 7 Setup DVD and boot into installation. After this select Repair your computer -> Command prompt. In the command prompt window, enter the following to repair your boot loader:
bootrec /rebuildbcd
After a few moments, it should detect your Windows installation and ask if you want to add it to the boot loader. Enter Y to add it, then exit the command prompt and reboot your computer when you’re finished.
You can restore the Windows 7 bootloader from a Windows 7 DVD.
The easy way is to boot from the DVD and use Startup Repair.
The slightly harder way is to go into the command prompt after booting from the DVD, and use these commands:
bootrec /fixmbr
bootrec /fixboot
bootsect /nt60 all
Of course you have to be careful when trying to replace the bootloader, as it can result in a failure to boot. But in your case, it doesn't work anyway, so you can try these commands.