When you enter the database host, are you running a site on a VPS our Dedicated SErver? Are you entering localhost?
I don't know if this is related but I did get a very similar issue a few months back and someone suggested to me to try entering 127.0.0.1 instead of localhost and that solved my problem.
I don't know if this has anything to do with your issues but I thought I would share my problem in the hopes that it might be similar to what you are having.
Best of luck