On this particular model, the first thing I might check is actually the trackpad. It’s easy to overlook because it’s under the battery. See if you get power if you unplug the trackpad. If so, pop the battery up and check to see if there’s any corrosion in the trackpad side of the connector, it’s fairly susceptible to even minor liquid contact in this model since the connector is close to the top edge of the trackpad and no protection from liquid entry through the gaps around its edges.
Otherwise, it’s probably safe to assume it’s a board issue. Which is still solvable in the right hands.