this is an issue routed in eityher of two places...1) malware 2) file corruption.
Please do the following:
Start > Run > copy and paste in:
You will need your XP/2000*Grinler disk. If you don't have it and instead only have a recovery CD, there is a work around. View the following link for a tutorial:http://www.updatexp.com/scannow-sfc.html
sfc - system file checker, retrieves the correct version of the file from %Systemroot%\System32\Dllcache or the Windows installation source files, and then replaces the incorrect file.
If you want to see what was replaced, right click My Computer > manage, expand event viewer > system.
If that has not solved the issue...then please run a free online malware scan with Panda:
Make sure you tick Disinfect automatically
under Scan Options
Save the log of the scan and if it has detected anything more then tracking cookies....paste it in to your next post ...let us know how you get on