Why are my keys "f", "r", "4" and "5" not working?

My laptop warranty expired about 2 years ago. I've had problems with keys "f", "r", "4" and "5" for a year now. These keys are next to each other. If I press one of those buttons let's say 10 seconds, the key usually starts working a little. If it doesn't start working, usually I press two of those buttons in turn and they usually start working. If the laptop fan starts making noise those buttons usually stop working. I have tried cleaning under the buttons but it didn't help. Is it possible that one certain electric circuit that responds to input from these buttons is malfunctioning? Is there some way to fix this? Thank you in advance :)