I'm not sure what might be causing your problem between your install and plugin. It sounds like it might be the plugin if you weren't having problems before using it. I wouldn't worry with the "Under Construction" stuff too much since WordPress has a setting where you can keep it from being crawled by the search engines.
My WordPress sites installed with this setting being defaulted to blocking the search engines, but if you need to change the setting, you can by doing the following:
From your Dashboard:
- Click Settngs in the left navigation
- Click Privacy in the drop-down menu
- Adjust the setting using the radio buttons provided
- Save your changes
I hope this helps you. Best of luck with your new blog!