|you do not need to format you hd|
just perform a repair installation
Enter the Windows XP CD into your computer
◦Boot up from the CD. See how to select boot device if you are not sure how to do this.
◦At the Windows Setup menu, hit Enter to setup Windows
◦Press F8 to agree to the End User License Agreement
◦Ensure that your current installation of Windows XP is selected in the box, and then press R to repair Windows XP
Setup will now attempt to copy all necessary files into your disk, reboot the computer and commence the repair installation.
At the end of the process, you will have to re-apply the relevant service pack and latest patches to complete the repair.
1.Change the BIOS boot order so the CD or DVD drive is listed first. Some computers are already configured this way but many are not.
If the CD or DVD drive is not first in the boot order, your PC will start "normally" (i.e. boot from your hard drive) without even looking at what might be in your disc drive.
Note: After setting your optical drive as the first boot device in BIOS, your computer will check that drive for a bootable CD or DVD each time your computer starts. Leaving your PC configured this way shouldn't cause problems unless you plan on leaving a disc in the drive all the time.
2.Insert your bootable CD or bootable DVD in your disc drive.
How do you know if a CD or DVD is bootable? The easiest way to find out if a disc is bootable is to insert it in your drive and follow the remainder of these instructions. Most operating system setup CDs and DVDs are bootable, as are many advanced diagnostic tools like the ones I discussed above.
Note: Programs downloadable from the Internet that are intended to be bootable discs are usually made available in ISO format. See How to Burn an ISO Image File to a CD or DVD for more information.
3.Restart your computer.
4.Watch for a Press any key to boot from CD or DVD... message.
When booting to a Windows setup CD/DVD and many other bootable discs, you may be prompted with a message to press a key to boot to the disc. To boot to the CD or DVD, you'll need to press any key on your keyboard (like the space bar) within the few seconds that the message is on the screen.
If you do nothing, your computer will check for boot information on the next boot device in the list in BIOS (see Step 1) which will probably be your hard drive.
Some bootable CDs and DVDs do not prompt for a key press and will start immediately.
5.Your computer should now boot from the CD or DVD disc.