A Repair Install will replace the system files with the files on the XP CD used for the Repair Install. It will leave your applications and settings intact, but Windows updates will need to be reapplied. Here is how to run an OS Repair using the Operating System CD in XP, Vista, or 7:Windows XP
1. Boot the computer using the XP CD. You may need to change the boot order in the system BIOS so the CD boots before the hard drive. Check your system documentation for steps to access the BIOS and change the boot order.
2. When you see the "Welcome To Setup" screen, you will see the options below:
3. Press ENTER to start the Windows Setup.
4. Accept the License Agreement and Windows will search for existing Windows installations.
5. Select the XP installation you want to repair from the list and press R to start the repair. If Repair is not one of the options, END setup.
6. Setup will copy the necessary files to the hard drive and reboot. Do not press any key to boot from CD when the message appears. Setup will continue as if it were doing a clean install, but your applications and settings will remain intact.Windows Vista
If you have a Windows Vista installation disc, you need to restart (boot) your computer using the installation disc. If you do not restart your computer from the disc, the option to repair your computer will not appear.Here is a step by step picture guide.
If you have a Windows Vista installation disc:
1. Insert the installation disc.
2. Restart your computer.
3. Click the Start button, click the arrow next to the Lock button, and then click Restart.
4. If prompted, press any key to start Windows from the installation disc. Windows 7
1. If a startup problem is detected, Startup Repair will start automatically and try to fix the problem.
2. If the problem is severe enough that Startup Repair doesn't start on its own and you can't access the System Recovery Options menu on your computer's hard disk, you can get to the menu and start Startup Repair by using the Windows installation disc or a system repair disc that you created earlier.