PS/2 keyboard partially not working

I have an IBM PS/2 keyboard that worked well until a few hours ago, the problem started while I was using my linux PC as I usually do. I tried to write something and then quickly found out that the B, N, /, Space, arrow down and Numpad minus keys were not working. I tried re-plugging the keyboard (when the computer was off) but that didn't help. I also tried disabling i8042.pnp in kernel options but that didn't help as the keyboard still doesn't work and it also doesn't work in grub. How do I fix this?

Question by Elperson on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.