Start at the battery. When the batteries short out they are done and you can't jump them to get the unit started. You could remove the battery cables and install bolts into the cables and jump to the bolts. Limited success with that procedure though. Most jumper cables can not handle starting the unit because of their length and gauge. If your battery checks out then clean your battery cables. top and bottom and battery post base. If you have a volt meter and a helper you can check for voltage drop across the battery and from the battery to the frame when attempting to start.
