Enable/Disable Task Manager

If your task manager is disabled and you want to enable it back.Follow these steps.

First,open your registry by typing 'regedit' in the run command.
Now,browse to the

HKEY_CURRENT_USER\Software\MicrosoftWindows\CurrentVersion\Policies\System

You should found a key value DisableTaskMgr

Now double click to edit it's value.

Change the value to 1 to disable task manager.
Change the value to 0 to enable task manager.

Good Luck