[Potatonator]

Last Saturday we got our kit of parts, which included two motors. Those motors worked perfectly fine when we manually turned them then for testing. After testing them, we built them into gearboxes, and then stored them in a box with other parts. Today (Wednesday, four days later), we took out the motors again, and they could barely turn at all. Nothing about them has been modified, aside from putting them in the gearboxes. Any ideas what our issue could be?

Thanks in advance =D

EDIT: Fixed a wording error.