The CPU is the board that contains the microprocessor but it will typically handle more functions than just that. The software is stored on removable chips, EEPROM or FLASH memory. This is the program that the processor runs to boot up, tell the LCD what do display and perform all functions. Basically, without the software, it doesn’t even know it’s an elevator.
Hopefully this is not the case, make sure all the chips are seated and the card is fully inserted. All these chips are highly susceptible to static discharge if applied to the wrong pins. It’s always a good idea to wear a wrist strap or, at least, touch ground before touching any boards.
