Although this is not a resolution, I also have had the same exact problem you are having just occure today on a Apex ADV-3750(Walmart's version of the ADV-3800). The video on the DVD side of the combo unit has gone completely blank. It still recognizes readable discs and will play them. I also can still hear the audio. It had an issue playing back a DVD where it was not still-framing, fast-forewarding, reversing properly. I stopped play, removed the disc and cleaned it, recycled power to the player and that's when it stopped showing a picture. I've no clue what happened or how to resolve it.
Nesaukee
September 2006