Reboot with the install disk and do the following:
When you see the Welcome to Setup blue screen.
Press R <Your screen will go black> Press "1" <Enter your admin password> <At the prompt type this, where D is your dvd rom> COPY D:\i386\NTLDR C: COPY D:\i386\NTDETECT.COM C: FIXBOOT <Press Y> <Then reboot>
Hope that helps.