It's working fine now because I scrapped the lot and started again. But I don't have my old database and, after about 18 hours on this, I am about to give up and archive the old forum and start afresh.
I tried restoring the database using PHPMyAdmin ... db all chopped into nice, manageable sections, then couldn't log in as Admin and when I logged in under another name, got a 404 error.
I created a test forum to see if I could get things working there, No luck.
I've read and re-read all the instructions I could find here, tried it all and am still unable to make the thing work.
For the sake of my poor computer (which is getting all the blame at the moment
) unless anyone has any bright ideas, I will have to throw in the towel.