Grasp the keyboard at the top (above the function keys). Turn it over and holding it at 45 degree angle, sharply tap the bottom of the keyboard casing (near the space bar) against the desk about ten times. You will see all kinds of junk come out. Clean that up, then test the keys again.
You will see all kinds of junk come out...
Sounds like you've seen my kid's keyboard. I swear, he won't eat or drink unless it's over that keyboard. I employ the same technique you mentioned...