I have a 120gb ipod with a bad screen (line going across it). I tried to replace it with an extra screen that I have (I believe this screen came form a 80gb ipod video). It powers on but shows nothing but a blue background then shuts off. I tested the extra screen in a 160gb ipod and it works perfectly. Is there some incompatibility with screens between models?

Continue to carefully hold the socket down while doing the next step. If the cable come off at the wrong angle it can pull the connector away from the board at the base of the screen.

Be extremely careful while doing anything around the screen. The slightest bit of pressure in the wrong direction and you will be replacing the screen along with the battery. I speak from experience.