If only specific keys are not working, it is likely that either there has been damage to the keyboard or a software function has been activated. Please firstly ensure that Number Lock is not turned on, via your Function keys.
If there is an issue with the keys themselves, the recommendation is to clean the device. Try and clean between the keys so that they can be pressed in properly. Do not lift the keys as they could be snapped off, instead use compressed air or a soft brush to perform the clean.