If the cable is damaged, yes it can prevent the LCD from working properly. The fact that it lights up does not mean that the cable is OK because there are several wires (6 if I remember) for power. But there is only 2 (TX, RX) for communication.
Have you checked that this cable is properly inserted into the sockets (both on the LCD and mainboard sides)?
I do not think so. They say this because the USB chip on the board is not well recognized when connecting to a USB 3 port and most of the time, it is not possible to connect to the printer with a USB 3 port. Have you tried with a USB 2 port?
Something is not clear: does your printer still working when you remove the USB cable?