@anncan , Belle, Most people do not realize DVD player like most devices require servicing/cleaning once in a while. So before throwing it away try giving it a good cleaning, below are some guides that will show how to remove the DVD players case and how to clean to help eliminate problems. Also it should be noted that DVD's can degrade over time, especially when not stored properly, the last link gives a good explanation of this. Try your DVD disc that are giving problems in another player to rule out damaged disc. There are also DVD cleaning kits available at almost any store that sells DVD,s that you could try, they will not clean as thoroughly as seen in the links though. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://www.dummies.com/home-garden/home-improvement/how-to-maintain-your-dvd-player/
[guide|4923]
https://www.youtube.com/watch?v=9NwX8-oTnRQ
http://dvd-players.wonderhowto.com/how-to/clean-dvd-player-135504/
https://www.lifewire.com/what-is-dvd-rot-1845719