Rebuild your boot configuration data.
http://pcsupport.about.com/od/fixtheproblem/ht/rebuild-bcd-store-windows.htm
That should do it.
You can also try a startup repair using your original disc.
http://pcsupport.about.com/od/operatingsystems/f/repair-installation-windows.htm
Try rebuilding the BCD first. That is done in DOS and should work.