Trains do not work Bachman HO

Question

After three years in a box we set up the train set last night and it does not work. The transformer gets slightly warm when plugged in but when moved into the forward or revesre postion the trains do not move or make any noise. Where shoud l I begin in trying diagnos and fix the problem? We don't even remember the configuration of how the transformer is to be plugged into the tracks.