If mythtv is working fine but mythweb fails, then edit this file:

/etc/apache2/sites-available/mythweb.conf

There is an entry for the password and if you have changed the password in mythtv it retains the old one
Code:
setenv db_server        "localhost"
	setenv db_name          "mythconverg"
	setenv db_login         "mythtv"
	setenv db_password      "*****"
Tony