If you have have the windows 7 cd:http://support.microsoft.com/kb/927392
Put the Windows Vista or Windows 7 installation disc in the disc drive, and then start the computer.
Press a key when you are prompted.
Select a language, a time, a currency, a keyboard or an input method, and then click Next.
Click Repair your computer.
Click the operating system that you want to repair, and then click Next.
In the System Recovery Options dialog box, click Command Prompt.
Type Bootrec.exe, and then press ENTER.
Choose /fixboot option