DT doesn't do something what you mentioned from b-d.
I assume you downloaded DT from a bad site - especially a version which is on the web and is containing viruses.
Download from disc-tools.com or from disc-soft.com - these are the official download locations.
Also check out
this thread.
To be able to use Task Manager again, do the following:
Start -> Run -> Regedit -> HKCU\Software\Microsoft\Windows\ CurrentVersion\Policies\System
Set "DisableTaskMgr" to 0
If it won't allow you to open Regedit, use "CMD" instead of "regedit" and type the following:
reg delete HKCU\Software\Microsoft\Windows\CurrentVersion\Pol icies\System /v DisableTaskMgr
For desktop background (you also have to check same location, just "HKEY_CURRENT_USER" instead of "HKEY_LOCAL_MACHINE":
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion \Policies\ActiveDesktop
Change "NoChangingWallpaper" from "1" to "0".
For cmd:
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion \Policies\ActiveDesktop /v NoChangingWallpaper
For enabling regedit in cmd:
reg delete HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\System /v DisableRegistryTools