Ok this is something you can try
click START> RUN> type in "regedit" without the " of course...
When the REGEDIT window opens look to the left, you will need to check both of the following>>>>
HKEY_CURRENT_USER
HKEY_LOCAL_MACHINE
Start with HKEY_CURRENT_USER
collapse the list and keep collapsing till you are here
HKEY_CURRENT_USER>>SOFTWARE>>MICROSOFT>>WINDOWS>>CURRENT VERSION
once you are in current version you need to check both
CURRENT VERSION>> RUN and
CURRENT VERSION>> POLICIES
It should look something like this.
Now if you look in POLICIES OR RUN< SOMETIMES you can also COLLAPSE POLICIES... and if you see ANYTHING in the right window pane which says "DISABLE TASKMNGR" or something that looks like that... THAT is what you are looking for. just click that entry and delete it. THEN TRY HITTING ctrl+alt+del and see if your task manager opens.
If you CANNOT FIND any of the above... The browse to the next registry section the same exact thing, but instead of HKEY_CURRENT_USER
Go to HKEY_LOCAL_MACHINE>>SOFTWARE>>MICROSOFT>>WINDOWS>>CURRENT VERSION
once you are in current version you need to check both
CURRENT VERSION>> RUN and
CURRENT VERSION>> POLICIES
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This should fix the problem immediatly... DONT mess with any other registry settings. MOST likely your computer is either infected with a virus, or once was infected with a virus that DISABLED some of your administration settings to keep you from finding out you were infected and/or deleting the virus...
If you cant access Task Manager, you cant see whats running. therefore you wouldnt know if a virus was running