Please Help – Can't Publish

I’m building my first WordPress site. I can publish my home page (http://www.authormartinroth.com/) but none of the other pages will display.

For example, I have tried to publish an About page (http://www.authormartinroth.com/about-martin-roth/) but get an “HTTP Error 404.0 – Not Found” message. It says the requested URL is http://www.authormartinroth.com:80/about-martin-roth/.

Can someone please tell me what I’m doing wrong?

Thank you.