One of my keyboard bottoms stopped working, Number 0 , Solution?

You may need to pop off the keycap to get under it to clean the junk that is causing your key to not work.

Here's a good writeup on how the keys work and how to pop the key cap off: Keycap removal & fitting There are a few YouTube vids if you want to see the process.

Once you pop the keycap off you want to be very careful on what you use to clean things here. I use distilled water for surgery stuff like dried soda or coffee or tea which had sugar added. I use a high grade of Isopropyl alcohol (85% or better).

In either case I use a cotton swap (Q-Tip) slightly damp as I don't want the liquid to drip down into the insides of the computer. Often I take the scissor part out to wash in a small container and then dry off before putting it back in.

For crumbs I use a soft paint brush and a can of can'ed air I carefully brush the keyboard area and then a short blast of air at a sharp angle to push the dirt out.