Be really careful when you unclip the screen bezel under the LCD; the tabs snap off really easily. Use a wide thin Phillips screwdriver to gently push on the tabs and lift the bezel up with your fingers. Hopefully that's where you'll find a loose connector, of which there are a few.

Getting to the motherboard's screen connector is more difficult, as you have to remove the top bezel. This involves unscrewing all the screws on the base (don't forget two screws hidden under the push-out feet), two near the ports, and one on the hard disk caddy/floppy drive casing.

(Yes I pulled apart three PB5x0s on the weekend)

JB