I have a Pioneer xv-htd540 dvd player and hooked it up to a 1080p TV, worked great then decided to play with setup screen and selected tv's 480 or better, now can't see or hear anything except a blue screen..

Try connecting it with either component cables (red, green, blue) or composite cables (yellow).

Is there a remote button for video format? If so, you can cycle through the options, without being able to see an on-screen menu, until you get the picture back.
Daniel