System restore blocked by group policy

Hello,
Recently my computer had been affected with virus. when i was working suddenly a pop up asking for installing the antivirus appearedon the screen and started installing even before my acceptance. It stopped all my application and startup files. I tried system restore option and successfully restored my system.

Now, two days ago again the same virus attacked my computer and caused me same issues. I tried to due a system restore again, but it throws an error " system restore turned off by group policy,contact system administator" i tried to turn it on, but there was no system restore tab in "my computer-properties".
i tried "gpedit" but it doesnot work. i tried "regedit" but it gives me an error "started working but stopped by some files".
I have windows-xp OS.

can someone help me to restore my system to a previous date and succeed against the virus?

Thanks,
Kris