If its not a laptop keyboard you will find that you can pop the keys off without affecting operations to a great extent. They don't have the tiny parts that break like a laptop one does.
Take a photo of the keyboard.
Pop every key off except the for the keys the size of tab, capslock, shift, spacebar etc - they have additional components that take a little more care to remove.
If you need to, push down the key next to it and lever the key off - with a normal key or screwdriver.
Once everything is off, use a brush, or can of compressed air to clean the keyboard surface, and a brush to clean the base of the keys itself.
Put the keyboard back together and you will probably find it now works, esp if the problem was a difference in how the keys felt when pressed