Does your machine have touchpad controls or pushbuttons? If it has pushbuttons, you're in luck because it won't be an expensive repair. If it has touchpads, then it could be a problem with one or more of the circuit boards and you won't be able to tell by any normal testing means with a multimeter. The touchpad machines have gone through a couple of circuit board revisions, and if one of the boards is bad, they must be replaced as a set.
The pushbutton machines are all switch/relay/diode logic, and everything can be tested with a multimeter. You won't find anything without sitting down with a schematic though. Genie puts the schematic on something like 6 full pages. Print them off, match the pages up and tape them together....then go from there.
Ohm out the control harness leading up to the platform controls first though. You could have an open conductor in it, or it could have been damaged by the boom being set down on it if it came loose from its tie-offs. Disconnect it from the platform control box and then follow it down to the base and disconnect that end also. Check and make sure there is continuity through each conductor.