Task Manager has been disabled by your administrator
Enabling Task Manager from Group Policy Editor
1. Go to “Start” -> “Run” -> Write “Gpedit.msc” and press on “Enter” button.
2. Navigate to “User Configuration” -> “Administrative Templates” -> “System” -> “Ctrl+Alt+Del Options”
3. In the right side of the screen verity that “Remove Task Manager”" option set to “Disable” or “Not Configured”.
4. Close “Gpedit.msc” MMC.
5. Go to “Start” -> “Run” -> Write “gpupdate /force” and press on “Enter” button.

Enabling Task Manager from the Run Menu
Go to Start –> Run and copy and paste the following and press OK.

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