All I can suggest is that you triple-check the connections. The trackpad is connected to the motherboard on most laptops by a narrow ribbon. Check that it's fully home in the connectors at both ends, and the clamping bars are clamping it how they should. If you disconnected the ribbon at both ends (not normally necessary) did you put it back the right way up?
If it is the trackpad that's died, you might be able to get a spare on eBay, or a dead laptop of the same model with a working trackpad that you can cannibalise.