The keyboard cable to the mainboard probably is loose or has dirty connections. Follow directions below for lifting keyboard off laptop and try to reseat this connector to clean its contacts.

You must push upward and sideways with your fingernail or credit card to loosen 7 hidden plastic latches one by one at the indicated arrows.

The keyboard ribbon cable is inserted in a black colored mainboard connector with a white or gray colored wedge slider to hold it in. The slider must be pulled toward the ribbon cable on each side to release the cable. Then push the cable back in and lock it by pushing the white slider on each side. Repeat this a few times to help clean the keyboard connector contacts. The ribbon cable is quite short and may be difficult to keep in the connector when you try to push the keyboard back down into the  normal position.

The whtie or grey slider sometimes breaks off. If this happens, you can use Scotch tape to hold the ribbon cable in the connector.