Fixed the virus issue.

Few weeks back my laptop was infected by some unknown Trojans/spy ware. The first impact of the Trojan or virus was to remove my administrator access to my laptop. When I try to open the Taskmanager or system registry, i got the message that my access to those modules are restricted by administrator.

Registry editing has been disabled by your administrator.
Task Manager has been disabled by your administrator.

I took my laptop to an authorized service center. Those guys couldn't figure out a solution for my problem. They simply said only formatting the hard drive will solve the problem. However I'm not in a position to format my hard drive. I may need another hard drive of 100 gb space for taking a backup.
When I googled for this problem, some site asked me to try opening the group editor(gpedit.msc) and change the settings through it. But this didn't help. Further refining my search, I landed in these pages which really helped me.

http://windowsxp.mvps.org/tweakuirest.htm
http://windowsxp.mvps.org/Taskmanager_error.htm

Using the REG.EXE console tool in the first URL helped me in getting the access to the system registry

Once I got the access the registry, I followed the 3rd method in the second url. This gave me access to task manager too.

Now every thing is in place. First thanks to the above site owner and Google.

Lesson learned:
Never turnoff your anti virus. NAV was making my laptop bit slow. So i turned it off. If I haven't turned it off I will not landed in this problem.

I'm thinking of saying good bye to NAV. Currently trying ESET Smart security (NOD32). The system speed is not affected by this AV. Also planning to try Kaspersky and bit defender. I believe I will choose one among the three.