another way is you can re-enable it from mmc (microsoft management console). hit button "start" and click "run" and type mmc on the field. after opening the console, click file>open then select a file named "gpedit" which can be found in the windows>system32 directory
then you can see a tree navigation on the left side. under "user configuration" tree click and collapse "administrative templates" and under "system" folder click ctrl+alt+del options, you should see on the right side there are 4 options, choose "remove task manager" and then right-click "properties" and then select the "disabled" radio button. that should be able to solve the problem

just something I learn long time ago when messing with workstation pcs