I can't seem to stay logged in and have to re-login every time.
I think I've done the right things but who knows?
Any guidance appreciated.

... and, as if by magic, the problem seems to have sorted itself out.

Thank goodness, I was trying to think what was happening!   

I show up as a Guest or Login but if I click on a discussion I find that I am logged in.
Not a problem, thanks.

Actually, that has happened to me too mate.  I'll look into it.  Cheers!