Usually this caused by a virus or your administrator disabled access to it.
Symptoms:
- A grayed out task manager when right click at Systray clock
- If you run taskmgr.exe directly via "Start Menu >> Run" or command line it will give you the following message:
Task manager has been disabled by the administrator
Fix:
- Start Menu > Run
- We need to access Group Policy Editor, type:
gpedit.msc - Navigate to: User Configuration > Administrative Templates > System > Ctrl+Alt+Del Options
- Double click "Remove Task Manager" and change its setting to "Disabled" and click Apply
- Double click "Remove Task Manager" and change its setting to "Not Configured" and click Apply and OK
- Restart the computer for the changes to take effect.
Good luck!