Q1:Keyboard and Trackpad stopped working

A: But before we do that how does the battery look? as a puffed up battery can cause problems with the cable. Was someone inside before this happened? One other possibility is a damaged logic board connector so when you take the cable off really inspect the contact pins didn’t get damaged on the board side and I would also check the cable end side as well. The battery is flat like the one in the pictures. I have this laptop from day one and I only opened it, after the problem. I will order the ribbon cable for a start as there is no visible damage on the logic board connector.

Q2: “A” and “D” on keyboard not working after replaced trackpad

Sounds like a bad keyboard the keys A & D share the same row line with S but they use different column lines! so Q & E should also be affected too, if not then the given keys are bad. You may need a new keyboard.