One of my computers says that the administrator has the task manager disabled whenever I press ctrl+alt+del

How do I turn it back on?

http://www.kellys-korner-xp.com/xp_tweaks.htm line 51 right hand side- enable task manager. Download, run and it should work again.
Then I would suggest reading the Hijack forum sticky notes and posting a log there. http://www.techhelpforum.com/forumdisplay.php?f=32