It could be dust, get a can of compressed air and try to clean it. My W keys worked sometimes but by the end, that sometimes was once every ten or so presses. Having to hammer key to get 1 response made me think it wasn't a software issue. I was forced to buy a new one as I needed a working keyboard for school.
If the bios is a scary place, some of the other suggestions I saw would equally be so - one was replacing the keyboard itself.
You might need to get it repaired.