I have an DR275 LG DVD recorder. For some reason it stopped playing DVD discs. But it will play anything else you put in it I have cleaned the heads switch it of by the power as well. What could the problem be? Thanks Karel

The laser mechanism has a number of optical components, not just the lens. There also additional fixed lenses and mirrors inside the laser unit which are very difficult to access. If sufficient dirt builds up on these components then the dvd laser may not work properly. Unfortunately it is very difficult (or even impossible) to clean these parts.
Another possible fault is that the CD laser is usually separate to the DVD laser and the DVD laser is no longer working properly, while the CD laser is still OK. In this case, the unit is definately not repairable without replacing the whole laser unit (not a readily available item and not likely to be cheap).
If the unit is out of warranty, your cheapest option is to buy a new DVD recorder.