DVD's that won't start up without prodding
 

Most of my DVD's work fine, but I have had problems with a few of them, and the problem is always the same.

I have a DVD-VHS system. Sometimes, I will put a DVD in, and nothing will happen. The screen that tells you that the DVD is loading does not appear. So then, without taking the DVD out, I put in a videocassette in the VHS slot, switch my remote control from DVD to VHS, and press "Play". The tape starts (naturally), and when I switch the control back to DVD, the disc is already loading and the disc's menu appears. After that, everything works smoothly.

The DVD's that do this are not defective, because when I try them on another DVD player, they work fine. And most of my DVD's load up and play automatically.

What could be causing this, and does it happen to anyone else?

Please post the same thread in only one forum.