Hello @Mcat12 — thanks for the reply. I managed to fix it in the end by uninstalling Unbound which I found was using port 53. At least I think it was Unbound. Something, anyway, was using port 53, but I wasn’t sure what it was until I found this:
After that Pi-hole was fine… But then I had a completely unrelated problem with the network connection to that computer and I had to put the project to one side.
Thanks again.