I am by no means up to the same level of computing as the others that have answered this, but I recently bought a DVD-burner (for TV) myself, and the advice I got at the shop was to buy DVD +R or +R/W, as they are generally supported by more TV-DVD-players than the -R and -R/W format. This also applies to CDs. From what I got told, the -format is generally more for computers and +format more for players.
It is however, somewhat concerning that it just happened after you had changed some settings. If you remember the old ones, maybe try to set them back? Also, I would advise against using Windows Media Player to do any burning. Nero is by far much better, as others have said.