It is possible that one of the connectors inside is disconnected. You have to open both sides by unscrew all the screws. Take care that there are differend screws in some holes. Dont mix them up. On one site thereis a battery. Check this one by metering if that one if working. Also inspect the driver printed circuitboard, if the connectors are all fitted.
On the other half there you will find the mainboard and the driver board too. Same story inspect for disconnected connectors.