do you know what type of unit you have? A non lit unit the screen would not light up, a front lit unit has a button on the back to turn the light on and off.
Can you see anything on the screen? Hold select while turning the unit on..do you get anything then?? Depending on the firmware on the unit, if it has one at all, you may not get any sound. So i wouldn't even worry about that at this point, the main thing is to get at least something on the screen.