How to play a dvd on my laptop?

So before all this happened I watched DVDs on my laptop all the time. It got a virus about two weeks ago. It was so bad that, everything on my laptop had to be cleaned out, and everything had to start over. Well now when I try to play a movie, it says that I need to download a DVD decoder, and I aptlyay for it. If it was alreay on there I dont want to pay for it again. It's an older laptop. It's a dell, I'm not really sure, my sister gave it to me. Is there anything I can do without having to pay for this?