Joe,
first try unplugging the keyboard and plug it back in into a different port, see if that does anything...
The keyboard might be worn out, as I go through keyboards at least one a year (this one already needing to be replaced).
What you may want to try is, first either take a picture (digital cam?) of your keyboard - or write down what key goes where (I don't know if there's a picture of the keytops anywhere online) to use as reference.
Before I go any further, I have NOT done this to the Apple Keyboard (but i have to a MS Keyboard) and I do not take responsibility of any damage to your keyboard (uh, worse than it is already?)...
Using a small flat-blade screwdriver lined in tissue as to not damage the keys, simply pry a couple of keys off from the bottom up - you might be able to remove the rest of them by hand after you remove the first one.
Compressed air would be great to get a lot of the gunk off, or a damp (not wet!!!) towel.
There are also some hex screws (?) on the bottom side of the keyboard, you may try removing those to get to the keyboard's innards to clean too (again I've never done this).
I strongly recommend just replacing the keyboard, they are not TOO expensive and I'm sure you'll be happier with a new one than you'll ever be with the one you have now, even if you can get it to work again (it'll still be stiff, have a "worn" feeling to keys, etc.)
I need to replace both my Mac's and PC's keyboards (both USB).
