the admin username and password are stored in the wa_settings table of the gallery database.
the first thing to check is that the server is properly configured to save session variables.
Use the session test page from the following thread:
showpost.php?p=23826&postcount=2
if the test fails, you will need to contact the host to have them fix the problem, it is most likely a bad session.save_path setting in the php.ini file.