Here's your answer
Most older DVD players do not play different formats such as +R or -R, etc... The one I have found that will play anything, has the most features, and the best buy for the money, is fortunately also the cheapest. You can get a "Truetech" brand DVD player for $20 + about $5 shipping by going to Target's web site. I have two of them and just purchased one for my parents and had it shipped to them. The thing will play anything and has a lot of features that our expensive Sony DVD player (which is now resting quietly in storage) did not have. Our Sony was also picky about what format it would play. You can also go directly to Target or Walmart and purchase one, but I find it is about $30. In any event, the thing is small and takes up very little space, looks pretty decent, and works like a charm. The only complaint I have is that the remote is pretty small, and contains so many buttons and features that I can't imagine anyone would ever use. Once you learn where your necessary buttons are though, you'll get past that aversion.
Best of luck, ry