Why doesn't my DMTech TV with DVD player read any of my dvd's?

When I first bought my DMTech tv's (2) with integrated DVD player they played fine for about 9 months then whenever I try to play a DVD in either TV, I can hear the whirring sound of the disc turning round then a message comes on screen 'NO DISC' I have tried re-loading the disc, lots of times, I have made sure the disc is in correctly, I have cleaned the disc and I have used a laser cleaner disc in the TV DVD player, on both TV's. The DVD's I am trying to play are shop bought ones so not copies or hired etc, I have tried the DVD's in other DVD players and they play fine, so it's not the DVD. It has happened on both DMTech TV's with integrated DVD player. Is this a common fault? Is there a way of repairing it? Is there a little tweek that I need to do to enable DVD's to play properly? I would be grateful for any advice before I throw both TV's in the skip!!! They are both about 18months old.