I recently cleaned a computer that had scores of spyware infections. I noticed after the cleaning there were still two problems:

1) I was unable to press CTRL-ALT-DELETE to bring up the mananger
2) The desktop properties were missing tabs

To restore these features, go into regedit and navigate to this key:

HKEY_LOCAL_MACHINE
SOFTWARE
MICROSOFT
WINDOWS
CURRENTVERSION
POLICIES
SYSTEM

Set the data for any desktop or task manager keys to 0 and that will restore their functionality.