gpedit.msc access denied!!

[vanishfire]

hi!
i have very strange problem.
(1) if i change task bar or start menu or desktop properties they are automatically changed to their default setting after reboot.
i think some virus has changed group policy.

(2) So whenever i try to run gpedit.msc to change group policy one warning displays saying:
you don't have permission to perform this operation.
( i logon as administrator )
description:Access denied.
so how can i access gpedit.msc?
plz help me.

i have win xp pro service pack 2
i m uploading two pic to which help u to know the problem properly.

[HoustonIT]

This type of behavior is usually caused by malware. I've had good success with Malwarebyte's Antimalware. It appears to fix the effects of an infection instead of just delete the files and registry keys:

http://www.malwarebytes.org/mbam.php

[vanishfire]

thanks!!
i have downloaded Malwarebyte,But is there anything else that i can do without that antimalware software(with changing registry!!!)?????