When you're having trouble with your Windows XP computer, often your only solution is to reinstall the entire operating system using a repair install. A repair install restores Windows XP to its original configuration, but leaves your documents and applications intact. To perform a repair install, you'll need your original Windows XP CD. In some cases, you may need the 25-character registration key that came with the CD.
Step 1
Back up any important documents and files to a CD or another computer before you begin. Reinstalling XP normally doesn't affect your files, but it's better to be safe in case you run into unforeseen problems.
Step 2
Insert your original Windows XP CD into your computer and restart the system.

Step 3
Press the space bar when you see the message "Press any key to boot from CD." The message appears for only a few seconds; if you don't press the space bar quickly enough, restart the computer and try again. When the computer successfully boots from the CD, a blue Windows Setup screen appears.
Step 4
Press the "Enter" key when you arrive at the Welcome to Setup screen, and then press the "F8" key after you've read the license agreement.
Step 5
Press "R" on the next screen, where "C:\WINDOWS\Microsoft Windows XP…" is highlighted. By pressing "R," you're telling the setup program to reinstall Windows without erasing your data. After you press the key, the program erases your old Windows files and begins reinstalling the operating system. This process will take several minutes.
Step 6
Click "Next" on the Regional and Language Options screen to accept the default U.S. settings.
Step 7
Choose your network settings on the Workgroup or Computer Domain screen. If the computer is part of an office network with a domain server, select the second option and enter the name of the domain in the field. Otherwise, leave the setting on the first option. If your office uses workgroups, enter the name of the workgroup.
Step 8
Click "Next" to complete the installation. After the installation is complete, your computer will restart and load the Welcome to Microsoft Windows screen.
Step 9
Click through the screens until you get to the Who Will Use This Computer screen, and then enter your Windows username. Click "Next," and then "Finish" to continue to the Windows XP desktop. Enter the 25-character key that came with the CD if prompted.