Tonight, at around 23:30 (so last night actually), I tried the "one-click install" feature from my service provider again...
If you look down a few posts you will see what happened last time I tried that. I am still trying to work out why I thought that was a good idea, and why I thought 23:30 was a good time to try it.
Anyway, things appear to be working now - that could be because I just gave up and removed Joomla and PhpGedView.