Letter "f" doesn't work on keyboard, but "shift F" does...

Running a full size (with num pad) wired keyboard on my 27" 2011 iMac and now the letter 'f' doesn't work.

Hardware issue? That is what i thought.

But why then can I get a cap F by holding shiy and the f key?

(fyi - i am typing the 'f' by pasting it, which is getting tiresome.)