How to Repair Missing Windows XP Files

Repair Windows XP Files with System Restore
1. Save your work and close all open programs. Click Start, then Control Panel, then Performance and Maintenance. On the left side of the screen, click 'System Restore.'
2. Select 'Restore my computer to an earlier time.' Click Next.
3. Click a date with a bolded number in the calendar on the left. Make sure this date is at least 1 day in the past. On the right side of the window, select a restore point. Click 'Next' twice to restore your system.
Repair Windows XP Files With the Installation CD
4. Back up all of your user files onto removable media such as CDs or DVDs. Find your Windows XP installation or recovery CD, and insert it into the optical drive that your computer can boot from. Click Start, then Turn Off Computer, then Restart to reboot your computer. When the 'Press any key to boot from CD' message appears, press a key on your keyboard. Press 'Enter' to start Windows XP setup, and press F8 to accept the licensing agreement.
5. Select the path of your Windows installation and press 'R' to begin repairing it.
6. Follow the instructions provided by the Windows XP repair program and finish the reinstallation. Go to the Microsoft website and download Service Pack 2 from their website, then visit Windows Update to install Windows XP Service Pack 3, critical updates and Internet Explorer 7.