The power seat system can be fairly complex. Depending on the model of Infiniti there could be a blown fuse, a blown fusable link, a bad circuit breaker, a defective control module, or both seat motors have gone bad. Under the hood locate the fuse and relay boxes, and remove the lid, which should have a listing of the fuses and what they operate. Locate the one for the seats and see if it is blown. If it is a plastic fuse it will be easy to tell, the "bridge" between the posts will have a gap. If it is a fuseable link it may look like a burned loop of wire, replace if defective. If it blows again there is a "short in the system or If the fuse is ok this may require a visit to a repair facility.