Okay.  You may need to do a repair reinstall of Windows.  You will need to boot the system from your Windows 7 CD.  There should be an option to repair or restore windows.  Try a restore first.  If that fails, do a repair.  Make sure your bios is set to have the CD/DVD ROM as the first boot device.  I have not yet had to do that in Windows 7, but I know a few folks who have and they told me it was pretty easy.  Just follow the onscreen instructions.