Reboot the computer with the Windows 7 disc in the optical drive. When you see the "Press any key to boot from CD or DVD" prompt, press a key so that the system boots into the Windows 7 install disc.
On the second screen of the Windows 7 installation, click on the Repair Your Computer option.
You should next see a window that says, "Windows found problems with your computer's startup options. Do you want to apply repair and restart your computer?" Select Yes, and the system will reboot.
Once again, boot into the Windows 7 install disc by pressing a key when you see the "Press any key to boot from CD or DVD" prompt.
On the second screen of the Windows 7 install disc, once again click on the Repair Your Computer option.
This time around, you should see a different screen. Choose the option "Use recovery tools that can help fix problems starting Windows. Select an operating system to repair"; highlight the Windows 7 partition, and click Next.
Select Startup Repair. The system will automatically reboot.
This time around, do not boot from the Windows 7 install disc, but instead allow the system to boot from the hard drive.
While booting into Windows 7, the OS will likely check the file system for consistency. Let it do this check. It might take a while—the larger the Windows partition, the longer it will take. When the check is done, the system will reboot.
On the next boot, the system should boot directly into Windows 7 without giving you an option for which OS to load.