When you right click on task bar, press Ctrl + Alt + Delete or Ctrl + Alt + Esc, you found that task manager option has been hide and it don’t work.

Follow these steps to active task manger option again-
1.Go to Start > Run or Window Logo + R, Type gpedit.msc and press Enter.
2.In the resulting window navigate to the folder.
3.”User Configuration” -> “Administrative Templates” -> “System” -> “Ctrl+Alt+Del Options“.
4.in the right side of the screen Select Remove Task Manager option.
5.Double-click the Remove Task Manager option.
6.Choose Disabled radio button in window then click apply and ok.
And now you can check your task manager option again

Tags: local group policy, Windows Vista