Right, let me start again. Further testing done.
I bought the replacement drive, same model as before - got same result, laptop didn't recognise it.
Borrowed of another laptop. Tried both my drives, old (supposedly dead) and the replacement in it, both work fine. Lots of life etc. Working perfectly.
So, what can you now suggest I do with the laptop, given this history, to make it see either of these DVD Combo drives?
and does anybody want to buy a combo drive 'cos it looks like I got one spare?