[Arran]

 Nine times out of ten or better, the motor is just fine, but the bearings in the motor or elsewhere in the changer are seized up due to petrified grease or oil from disuse. It's either that or the power switch is buggered up in some way such that the motor isn't receiving and voltage, but that should be easy to bypass for testing purposes. It's much more common for the cartridge to be dead in a 1940s record player then the phonograph motor, Rochelle salt crystals are notorious for disintegrating over time, this may have one of the magnetic cartridges though since it's likely a higher end machine included in an early radio-TV-phono combo unit.
Regards
Arran