iPod Nano 6th Gen_New Screen - but still black (shows up in iTunes)

My iPod Nano 6th Generation had a black screen so assuming it was broken I bought a new one. However having now connected a new screen the display is still black. When connected to my iMac the iPod shows up in iTunes and appears normal. When I put on headphones I can hear the 'bup, bup, bup' when I press either the plus or minus buttons for the sound. Does anyone know what I can do next to try and get my screen (old or new) to work?