"Disconnecting and connecting back the narrower cable", do you know what color it is? Also, is it towards the top or bottom of the tablet?
The orange one. There is a big square battery right at the middle. Two cables run across it, above it, vertically. First one is wide and metal-colored, the second is narrower and orange. I reconnected the orange one at the top - there's a small metal rectangle connector, sealed with a piece of grey duct tape. I took off the tape, pulled the connector up to disconnect, then clicked it back down to connect. Turned on the device, it loaded as it should, all good.