Fix #3: Replacing the Keyboard
If none of the first two fixes did anything for you, unfortunately you'll probably just have to replace your keyboard. Notebook keyboard troubleshooting doesn't often end up at this extreme, but in some cases, drastic times call for drastic measures. If you don't know much about computers, you should really just take the whole thing into a professional to have the keyboard replaced. If, however, you think you know what you're doing, buy a replacement keyboard and get out the screwdrivers.
The exact keyboard you'll need to buy will vary, but on notebook computers, the actually replacement process is remarkably easy. Unlike on a Mac, you can pop the keyboard out without taking the whole thing apart in most cases, and the whole ordeal shouldn't cost you more than $30-$40 tops. If you have an older computer, you could really get away with something for as little as $15, not including shipping.
If you replace your keyboard to no avail, then unfortunately, I have no more advice for you. It could be your motherboard is having problems, and at that point you should bring your notebook to a professional, have them look at it, and get your computing life back on its feet as quickly as possible.