1. Have you tried a different A/V cable? Is yours damaged in any way? 2. Is the connector on the board nice and secure (it may have worked itself loose after all these years.) 3. If 1 & 2 don't work you might have a failure in the logic board (specifically the graphics section). Hope this helps.
Make sure you keep the small plastic divider (the little piece of transparent plastic film) in its place, or else your new power supply may find itself with a "grounding" sensation.
