Thanks Julien.
I have the disc drive hardware on my PC, it's the software I'm after.
When I ordered this Dell, I opted for a Blu-Ray drive because it was quite a cheap option to add. The supplied software to play Blu-Ray discs was Cyberlink Power DVD 9.5. However, it's never worked properly, and like an idiot I never got round to sorting it all out while the computer was still under warranty. I've since used up all of my three allowed downloads in an attempt to get it to work and patch it up to date.
I asked around on the Dell forums and it seems there's no way they can do anything about it because I'm out of warranty, they won't even repopulate my downloads. However, one of the guys in there took pity on me and sent me an older version of Power DVD (which I've patched up to date) but this fails to play some of my newer discs.