Windows Task Manager is a inbuilt program where you can check what processes are currently running on your computer system, you can also set priority of these processes. This is very helpful when you have to start or end any task or process forcefully. Task Manager can also be used to monitor RAM usage by CPU and its performance .Viruses and trojans can disable your Task Manager and you will get an error message :-
Different Methods to FIX Task Manager
Method 1: By Enabling it Manually
Open Run command [Win+R].Type gpedit.msc in it and click OK.
In the Right window panel look for the Remove Task Manager and Double Click on it.User Configuration>Administrative Templates>System>Ctrl+Alt+Del Options
Select Not Configured option and click on OK button.
Method 2: By Changing the Registry Settings
Open Run command [Win+R].
Type regedit and click OK.
Now expand Registry Keys as
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
In the Right window pane look for the DisableTaskMgr. Right click on it and click on Delete.
Confirm the Delete message and your Task Manager will available once again.
Method 3: Task Manager Fix
Task Manager Fix is a third party freeware utility to fix the Task Manager which is Disabled by viruses/Trojans. This will not effect any of your other registry settings.