DVD Problems

I have a 2002 WB edition venture. The dvd player works great if you put in a home copy dvd. If you use a store bought dvd then it will not work. I call a stereo place and they thought it might be a region code problem and said the dvd needed to be reset. I called one chevy dealership and they had no clue. I called another stereo place and he tried to reset the radio by pressing the hr and min buttons together for 10 sec. The radio said "no update" and it didn't reset the radio and it didn't fix the dvd. I called another dealership and they want me to bring it in so they can figure it out ( they had no clue either ). I don't want to pay an arm and a leg for someone to just figure it out then my other arm and leg to fix it. Does anyone know how to reset the radio or dvd player?? Or better yet what the heck is wrong and how to fix it. Thanks Aaron