DVD/ DVD Player Not Working

So I have a Mac mini that I use quite frequently on the day to day. A few months back, I hooked up an external DVD player to my computer and it played 'The Office' (a CBS television show) just fine. One day, I went back to an older season to rewatch some episodes, only to find my DVD drive saying "supported disk not available". Mind you, this disk I was trying to play has worked and ran very smoothly before, and then all of a sudden it ceases to work. My Mac mini doesn't even recognize the disk and it had just recognized it the previous day. Can someone please try to help me and figure out why this issue is happening?

(I've rebooted my computer and am up to date regarding software updates. I don't really want to go through the trouble of having to burn the DVDs individually, but if it comes to that, I will try to do it)