It's a common problem but now you must identify your new pest so you can remove it and repair the damage.
Try HOUSECALL.
Bob
When I click CTRL+ALT+DEL then instead of the Task Manager, a message appears:
"Task Manager has been disabled by your administrator!"
I'm the administrator and it happened a few weeks ago, but I had it when I fisrt got the computer. I know >>I<< didn't disable it.

Chowhound
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