If it is a regular keyboard (As opposed to a keyboard built into a laptop), you can try removing each key and cleaning underneath. Sticking a butter knife or something else reasonably stiff but dull under each key and "levering" will pop the key right out. Once clean, you just pop it back in. Don't do too many keys at a time, however, or you might forget where they all go. 😀 I'd say just get a new keyboard, though. They are fairly cheap and cleaning the thing key-by-key is going to make you want to kill yourself. 😛 I doubt WD-40 is going to do the whole job; something has likely caked up under the keys and will be difficult to remove with just a spray of the magical lubricator.
