If your system is currently running Windows, you can perform a re-install of the OS. In other words, you can install Windows over itself. This is often referred to as an in-place upgrade.
When you perform this type of installation, Windows XP is reinstalled to the same folder. Typically you would perform this type of installation if you were unable to boot into Safe Mode or if you were unable to repair an existing Windows installation.
To reinstall Windows XP by using Windows XP, follow these steps:

1. Start your computer and log on.

2. Insert the Windows XP CD into your CD-ROM drive.
3. On the Welcome to Microsoft Windows XP page, click Install Windows XP.
4. On the Welcome to Windows Setup page, click Upgrade (Recommended) in the Installation Type box (if it is not already selected), and then click Next.
5. On the License Agreement page, click I accept this agreement, and then click Next.
6. On the Your Product Key page, type the 25-character product key in the Product key boxes, and then click Next.
7. On the Get Updated Setup Files page, select the option that you want, and then click Next.
8. Follow the instructions that appear on the screen to reinstall Windows XP.

Once the re-install is complete you will once again have to install the latest service pack and any other updates that your system requires.

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