Windows 7 and Vista
1. Reboot your computer with the Windows 7 installation disc inside the computer's disc tray.
2. Select your desired language from the menu and click the 'Next' button.

3. Select 'Repair your computer' from the menu that appears. Select your version of Windows 7 from the menu and click the 'Next' button.
4. Click on the 'System Repair' option in the menu. The computer subsequently performs a system repair and then automatically restarts.
Windows XP
5. Insert your Windows XP installation CD into the computer's optical drive and boot the computer.
6. Select the 'Boot from CD' option when prompted on the screen. Wait for the 'Welcome to Setup' screen and then press the 'R' button to enter the 'Recovery Console.'
7. Enter your administrator password into the field when prompted on the screen and then press 'Enter.'
8. Type 'recovery console commands' into the command prompt and press the 'Enter' button to view a list of the commands that you can use.
9. Select the 'System Repair' tool from the menu and press the 'Enter' button. Wait for the computer to repair itself and then restart automatically.