I have some troubleshooting steps for you, first can you try to put the DVD into a set top box DVD / Blue Ray player or even a Xbox or Playstation if you have one in the house?
Inspect the reflective surface of the Disc in question, any scratches or blemishes? If so I have in the past made a damaged disk readable by polishing the relective surface with tooth paste, click or tap here for more info on that.
If the Disc is then made readable you will need to make a good copy of the Disc using software such as this.
Was this a store bought DVD or something made for you by someone else? You may very well want to try another media player such as Windows Media Player.