Sometimes you may encounter DVDs that won't play back on a specific machine. With homemade DVDs it can be an issue of DVD+R vs DVD-R compatibility (or lack therof). It's often trial and error. Laptop/PC drives will tend to play back more than standalone players IME.
I've had my MWD220GA for more than 5 years and it has played everything we put into it. However, now it won't play a regular, commercially bought DVD from 2005. The disc is not Blu_Ray. It is a Barbie movie that has an option for playing with or without 3D. I have 2 of the same discs because one was a duplicate gift. The machine will not play either one. It also had a hard time playing the same movie from the library, but we did once successfully get the library disc to play - but have never been able to get either of our personal discs to play. Anyone have any ideas? Will this old, cheap DVD player just not handle a 3D capable disc? The discs both play just fine on our 3 year old laptop and on my sister's DVD player which is as old as mine.