I always use the "Tab" button on my keyboard to open my character menu. I was just riding my horse from Whiterun to Windhelm when I realized suddenly that I couldn't open my menu. Tab doesn't do anything anymore. I tried going into setup/controls and reassign the tab button but whenever I push tab it's as if the button on my keyboard just doesn't work.

I tried quitting Skyrim and using Tab in a notepad and the keyboard button itself DOES work... just not in Skyrim. Skyrim isn't recognising it. Did I do something wrong or hit a wrong key?
Would anyone have any idea how to make the TAB work again?