There's a pretty good chance it's a blown power fuse. If I remember right it's on the SCR panel under the floorboard. The panel swings up on a hinge so you can work on it. There will be a single bolt that holds the panel down. Look for a flat 400 or 500 amp fuse.

Then tell your operator to stop sliding extra heavy loads. If the machine won't pick it up you need a bigger machine.