For whatever reason there isn't as much activity for the WMS-550 machines as the WMS-40X and the Bluebirds models. I've not had my hands on a WMS-550 so can't give much advice, sorry. Hopefully someone that knows about WMS-550 can offer some ideas.
Since the machine was working before it was moved the obvious thing to check would be all cables and connectors, power supply connections, power cord coming into the machine, etc. You can remove the circuit boards from the card cage and reinsert them. Sometimes when machines are transported they are laid down on the back or side. This allows any loose stuff inside the machine to jumble around and land anywhere. If that loose stuff is a metal coin, screw, washer, etc then it can cause an electrical problem by shorting something out. That stuff can get underneath or on top of circuit boards and inside power supplies. If the machine has fuses they should be checked.
You can post photos of anything you have questions about, or if something doesn't seem right. The card cage is the metal box that contains the main circuit boards for the machine. These boards slide into the card cage and plug into a backplane board behind the card cage. There is a door on the card cage, and originally the door would have a security switch so the machine would know and record when someone opened it. This is a security thing required by the casino. Also on the card cage door is a pushbutton switch. This is for getting into the machine's builtin Test/Diagnostic menus system. Do you have a manual for your machine?