An Anti-Virus alone cannot do you good.
- If you really want to repair your Windows Installation free of Viruses then you would have to do some work.
I recommend Avast! as this is the ONLY Anti-Virus that I have yet to become bored of and/or tired of. Keep in mind; Some viruses are detectable but there cleaning and removal might take more then just an Anti-Virus. For example; some viruses infect your registry and System "hidden" files that can go undetected by any Anti-Virus.
- One such virus I have recently experienced is INF: Autorun-C [trj]. Believe me... I am in Love with this trojan! :D.
It's the best Virus I have so far to encounter with the exceptions of botnets (Likes of Storm botnet :D) ofcourse..
The Autorun-C enables the System Restore Points (if disabled) and even leaves itself in it SO that if you ever happen to Restore your PC it would be there AS iS!.
It required some searching on the NET "":D"" as Avast! was able to DETECT it and Block it temporarily BUT Avast! was NOT able to detect its SOURCE files which associated themselves with 'explorer.exe' and Critical boot files such as 'ntdetect.com'.
In your case too; The virus has disabled your Registry, taskmanager etcetera...
Download ' UnhookExec.inf ' ; Which would most probably be able to ""UNHOOK"" your Registry and the things.
Even if it manages to UNHOOK you; there is very less you can do about.. I recommend you to "REPAIR" your installation of Windows and then re-try installing an AntiVirus suite; I am again recommending Avast! due to it being Free and due to its higher update ratio AND due to its nature of being more ""ANTi"" then any I have tried.