Alt-tab switches windows between open applications/folders. So I'm a bit confused by Alt-tab-control? I tried that on mine just incase I was missing something and nothing happened.. So what are you really asking? Task Manager is brought up Control-Shift-Escape or in non domain XP systems Control-Alt-Del.
You haven’t told us what OS you have. Before posting questions you are expected to give your main system specs.
As for opening the Task Manager, if you are using XP, try the alternative procedure: right click on systray (the clock area) at a clear point above the icons and select Task Manager.