Vista - Losing administrative privileges something like Nidma virus

Hi,

This is Cherag here, running Vista Ultimate x64 on a Intel Core 2 Duo based system with 4 GB ram. Suddenly I seem to have lost administrative privileges on the machine, noticed it when i wasnt able to start up the "Task Manager" (either thru Ctrl+Shift+Esc or right click on start menu-task manager and its grayed out, or Start-Run-Task Manager gives error "Task Manager is disabled by the Administrator"). Same thing happens with Regedit, i get a similar kind of error.
Let me tell you the things that I have tried -

First of all, i ran a complete antivirus scan on all the drives. By the way, even my AV, NIS wont start up automatically, and manually also it wont start. So i had to start and use it from Safe mode with Networking, where all it could do was a complete scan. However, it didnt report any viruses.

Next up i ran the complete system scan of Windows Defender which is updated regularly, however nothing reported from its side.

Then i downloaded a utility from Symantec called FixNimda.com and ran it, but it didnt find the Nimda virus as well. Also downloaded and ran a McAfee Stinger, but that found a couple of viruses, trojans mainly, and deleted them. but still i cannot open either task manager or regedit.

Next step i found out that i could use the gpedit.msc so manually tried to enable the task manager and regedit, which worked, but as i found out, only till the time its open. the moment i close out of task manager/registry editor, it again gives me the same error when i try to run it...

I would also like to tell you that ever since this thing has affected my computer, its become quite irritatingly slow, the CPU utilization keeps staying at 100% and Physical Memory utilization above 60% all the time even when there are no programs running. This i have seen from the Sidebar's Gadget of System performance...

I am sure this is the activity of a virus...however the antivitus systems dont report anything like Nimda or stuff...Any suggestions would be welcome...

Do this: boot into vista disk or recovery partition restore to a point before corruption of User account occured, then follow below steps.
note- consider NOD32 4 (it has self defense to prevent Viral corruption, and is better than Norton.)

System Restore
System Recovery Options

The Best antivirus/Antimalware Program currently Available

I suggest IE8 with has built in antimalware/antiphishing and smartscreen

Try these:
ESET SysInspector

Download and Install NOD32 4
Free Antivirus Download from ESET

Run Windows Defender (full scan)
Start> in search bar type defender>click program

run Malwarebytes (this will detect polymorphic malware)
Malwarebytes.org

note-Malwarebytes
This is a On demand Scanner only (real time detection mode disabled in free version)
This is a specialized tool specifically targeted at polymorphic Malware, and as such is not very effective against other malware threats. It is also meant to be run in conjuction with installed Antivirus- not as a standalone app

further note-
Chances are you may have suffered Windows corruption that only a restore/repair/re-install may fix.
barring that, and you use the above tools to clean your system, you can improve speed and performance here:
How To Make Vista more responsive and faster

Thanks for the reply...

i am trying ESET SysInspector and ESET Antivirus...

Will give the Windows defender full scan a skip coz i had done it before posting here itself. also i have downloaded, installed and run Super AntiSpyware and Comodo Registry Cleaner which themselves found a lotta junk and got rid of it...but still nothing that makes the task manager comes up.

And regarding the Vista slowing down, that is also related to this problem only, not only for the fact that its happened alongside with this issue. I have dual booting configured, and the XP installed is also showing the same symptoms...No Admin rights, frequent frozen screens etc...and that is installed on a different physical drive...so i dont think repairing vista will work here...