Some Viruses disable your gpedit.msc and you are unable to open the Group Policy Editor and also any Microsoft Management Console program.
When you open the gpedit.msc from run or services.msc you will get the following warnings.
I am listing two solution to this problem
Download and install Microsoft Management Console 3.0 for Windows XP.
Download the Smart Virus Remover.
Smart Virus Remover (889.9 KiB, 851,382 hits)
Run it and double click on the tray icon, click on Restore Windows Default Settings
Check the box Enable gpedit.msc and click Apply. You are done
Please let me know if this solves your problem.