Have you chaged anything lately, including, hardware and software and patches? What OS, IE version, keyboard (101)?
Check the that in Control Panel, Regional Options and Keyboard (Input Locales & Hardware) are correct. Check the same in Office app's, > Tools > Otions.
Check that any of the additional function keys/hot keys on the keyboard haven't been remapped.
Hunch, try repairing IE. (You may have to re-apply patches)
