Is it hotswap or are the switches soldered into the board? If the former then yes, first thing to try is re-seat the switch in the socket, check that a pin on the switch isn't bent (and thus not inserting into the socket at all). The second thing to check (or first if soldered) is, using a multimeter, check continuity between the switch and its row/column and between the switch and its diode and check that it is working.
In either case, if re-seating isn't enough, corrosion or oxidation could cause the behaviour. If hotswap, check for corrosion or oxidation on the switch contacts and the hotswap socket. gently try to remove any layer of oxidised material with something lightly abrasive like sand paper, or even just insert and remove it a few times to try to rub it off. Clean with isopropyl alcohol. If still not working try to reflow the solder joints.
If all that fails you may need to run a small wire to fix a broken or corroded connection but that's unlikely I'd imagine.