taskmanager in "Windows" folder
If your problem is that Ctrl-alt-delete is no longer opening tskmngr., you may be able to open it from the "Windows" folder-(double click "My computer", then on "C" drive, then on "Windows" folder--there's a taskmanager icon there.
This began happened to me at one point-don't know why-and the above worked. Ctrl-alt-delete began working again at some point-again , don't know why.
good luck