Wenjen
I think you may have to run System File Checker to do a repair of your system. Here are the instructions. (Before you do this, I want you to wait and get a second opinion.)

SFC /SCANNOW
Goto START and then select RUN and then paste the above command on the run line and hit enter. Make sure the WinXP disk is in the
CD Rom Drive. This will check the system files against the original install and make sure none are missing.
You will need to run Windows Update after this is completed.