Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
The first thing to try is, to take an air compressor of the type used for filling tires, and blow air into the keys - especially between the key that is not working and the adjacent keys.
Then hold down the adjacent key on either side, one at a time, of the not-working key, and blow air into the crack opened between the keys that way.
Repeat this process for all defective keys. See if that straightens out the problem, just by itself.
(If it does cure the problem, well and good! and please rate my answer in that case.)
If it is not cured, even if it is improved, let me know, and I will advise you further toward a complete cure. Thanks.