Run the System File Checker
Go to the Run box on the Start Menu and type in:
sfc /scannow ( sfc if not reconized)
This command will immediately initiate the Windows File Protection service to scan all protected files and verify their integrity, replacing any files with which it finds a problem. You will need your Windows cd.
If that does not resolve your issue you may have to do a Repair Install
Configure your computer to start from the CD-ROM drive. Then insert your Windows XP Setup CD, and restart your computer.
1.When the Press any key to boot from CD message is displayed on your screen, press a key to start your computer from the Windows XP CD.
2.Press ENTER when you see the message To setup Windows XP now, and then press ENTER displayed on the Welcome to Setup screen.
3.Do not choose the option to press R to use the Recovery Console.
4.In the Windows XP Licensing Agreement, press F8 to agree to the license agreement.
5.Make sure that your current installation of Windows XP is selected in the box, and then press R to repair Windows XP.
6.Follow the instructions on the screen to complete Setup.
If you have xp sp2 installed it needs to be incorporated into your xp disk or it will not offer the repair option only the clean install.
Slipstreaming Windows XP Service Pack 2 and Create Bootable CD
You may also have some type of spyware/malware installed, follow these steps also
First Steps at Removing the Malware and Posting your Log