Try running SFX.EXE, if this doesn't work you will need to do a repair installation.Guide Overview
The purpose of this guide is to teach you how to use the System File Checker (SFC) to examine and repair corrupt operating system files.
In doing this, the SFC tool may replace some of your files that were updated by Windows Update. The only way to check this (and to update any of the files) is by visiting Windows Update and allowing it to check your system for updates and update as needed.ReferencesDescription of Windows XP and Windows Server 2003 System File Checker (Sfc.exe)
Microsoft Windows XP - Repair overviewInstructions
1. Locate your Windows XP installation CD. If you don't have one, you'll need to locate a directory on your system that's named"i386" (without the quotes). This directory may be on a hidden partition on your hard drive.
2. Go to Start, then to Run, and type in "SFC.EXE /SCANNOW" (without the quotes - and with a space between the SFC.EXE and the /SCANNOW). Then press Enter. (For VISTA, go to Start and type in the above information, then go to the top of the box and right click on SFC.EXE /SCANNOW and select "Run As Administrator")
3. The program may (or it may not) ask you for your Windows XP installation CD - please insert it at the prompt. If it doesn't ask you for the CD this means that it wasn't necessary to replace any files.
4. In the event the the system asks you for the CD, you must visit Windows Update immediately after the scan is completed (Please note that there won't be any confirmation dialog - the program will just exit without telling you anything).
5. If this doesn't repair the problem with your system other troubleshooting procedures are required.