I have replaced the MB in this laptop, the original had liquid spill. The keyboard and the mouse pad are dead on boot. Looking for possible causes.

Probably a loose or broken cable. Check the cable that goes from the touchpad to the motherboard, and make sure there aren't any folds in it. Make sure it's inserted in the slot on the MB straight, and that the little tabs are down... it's real easy to not get it in straight.