The inbuilt DVD player in my smart TV stopped working so I bought a stand-alone DVD player and plugged it in. It worked for a few days but now says “No disc” on the screen where there is one. What’s the fault with?
A 'no disc' message can only be generated by a DVD player. (Your TV set doesn't 'know' that you've plugged a DVD player into it; it just knows that there's an external source in use, which could be something like a Sky set-top box as far as the telly is concerned, so it certainly won't give you a mesage relating to DVDs).
So it's your external DVD player which is faulty. (NB: I'm assuming that you're trying to play a shop-bought DVD. If you're trying to play a DVD recorded on your computer then it might be that the player doesn't recognise that type of disc).
Yes, it's brand new DVDs straight out of the packing, and I have tried several different ones, and each time they aren't recognised. It's just so annoying as I've just bought this new DVD player and I expect it to last longer than 2 plays!