Task Manager has been disabled by your administrator OR Reenable Task Manager in Windows

When you try to open Task Manager, the following error may occur:
"Task Manager has been disabled by your administrator"

Method 1

Click Start, Run and type this command exactly as given below: (better - Copy and paste)

REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f
 
Method 2

Download and run this REG fix and double-click it.

Method 3

Click Start, Run and type Regedit.exe
Navigate to the following branch:

HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies\ System

In the right-pane, delete the value named DisableTaskMgr
Close Regedit.exe

Method 4
Click Start, Run, type gpedit.msc and click OK.

Navigate to this branch:

User Configuration / Administrative Templates / System / Ctrl+Alt+Delete Options / Remove Task Manager

Double-click the Remove Task Manager option.
Set the policy to Not Configured.