Thanks for pointing me in the right direction. As a matter of fact I have bought PowerDVD and it plays my DVDs. That is unless I try to play from my hard drive in which case it asks for a product key, and then closes down when I enter it.
I had mistakenly thought that it was copy protection rather than a problem with my PowerDVD installation.
I've downloaded media player classic which seems just fine. Haven't yet worked out which file to click on to play it like a DVD but that's another day's tooling around!