No idea about the login problem, but the problem with editing and posting stories has been discussed several times before. See here for a workaround.
Since you switched hosts it looks like your new hosting service is running a different setup than your old one. If you could figure out the differences and what exactly causes the editing of stories to not work, we would be very grateful since this seems to be a common problem (though it really seems to be a problem with the server setup).
bye, Dirk