|If you have tried most of the recommendations and it no longer can read DVD's (after trying multiple ones) then the DVD read head is bad and the drive will need replacing. The CD'd and DVD's are read with different optical heads and much of the circuits and one side can go bad while the other still works.|
If you rarely use the DVD feature, consider getting an external DVD drive that plugs in via USB (they are not expensive) but if you use it more regularly like watching movies, etc. then replacing the drive would be a better choice for you.
You have to be a little bit crazy to keep you from going insane.