hi had similiar prob,in mine it was because it needed cleaning bought a dvd drive cleaner(the one with the brushes works best)had to run it about 10 times but that done the trick and my drive would play rw again, good luck bluey
dvd + & dvd - are two different formats - you must have the correct formats for your player. However, most moderm player will support both types. However, you also nmeed to check that the reader supports the software formats of your files.
The most likely reason is that your disk has not been finalised. When burning a dvd you normally get the option to Finalise the disk i.e. Close the disk so that nothing else can be burned to it - if the dvd is not closed then it will not play on a normal dvd player, only on a PC.