MacBook Air keyboard doesn't work

I have a MacBook Air from 2014 (1,8 GHz Intel Core i7 processor) . Suddenly, one year ago the keyboard started to do something strange. The row of letters q-p didn't work sometimes but all the other letters worked properly. First I noticed that holding down a bit more strong the keys q-p I could type but now it doesn't work at all.

Now I have to type with a wireless keyboard because I haven't found the solution yet. Sometimes all the keyboard works but only 5 or 10 minutes and then the row of letters q-p stops working. Does anyone have had this problem? Is there a way to reset the keyboard or something like this? Is really expensive to fix a problem like this in an Apple Store?

Thank you.