Here is a little helper if your Webmin does not respond.
Just run this command from the command line and it will bring the webmin service up again fresh.
# /etc/init.d/webmin restart
Following messages will appear after running that command.
# Stopping Webmin server in /usr/share/webmin # Starting Webmin server in /usr/share/webmin
After a fresh restart the Webmin server should be running again.