Insert your Windows XP disk into the CD-ROM and reboot your computer. Once your computer starts booting up you should see a message “press any key to boot up from CD-ROM” - simply press any key on the keyboard.

If you don’t see that message and your computer doesn’t boot up from your CD-ROM but from your hard-drive instead then you should
change the boot-up sequence from your BIOS - reboot your PC and press DEL to enter the BIOS setup screen. Make sure that you specify your CD-ROM as your first boot up device.

Once you manage to boot your PC from your CD-ROM at the “Welcome to Setup” screen press ‘R” to start the recovery console. If you have more than one boot systems, choose the installation that you need to access by pressing 1 for the first one, 2 for the second one and so on. Press Enter then type the admin password and press ENTER again (or simply press ENTER if you haven’t set up administrator password).

You will be taken to a DOS-like screen that says:
C:\WINDOWS>

or something similar, type format followed by the drive you want to format and press ENTER, so if you want to format your c drive then type:
format c:\
and press ENTER.

WARNING - ALL YOUR INFORMATION WILL BE DELETED FROM THE HARD DRIVE YOU WANT TO FORMAT!!!

Wait until your drive is formatted, then reboot your computer (with the Windows XP disk still in the CD-ROM) and follow the instructions in order to install Windows XP.