You need to go to tools>Customize>Keyboard and choose "view" from the drop down "Category" menu in TeXnicCenter. Under commands, locate "Full Screen" and add your new shortcut combo. I have Ctrl+F11 for mine. Once you are done, click "Assign" and then "Close". Now Ctrl+F11 (or your shortcut of choice) will help toggle between full screen modes in TeXnicCenter.
Edit: Oops...

I see I have gone completely off topic here. This helps only if you already have the short cut set up. My bad. Excuse me for being a noob.
