I'm not sure how this happened, but I was trying to set up a simple landing page while I work on my site, using Twenty Ten. I changed the background color, site title header, and header image in the CSS. I was trying to figure out also how to make my blog.mydomain.com appear as http://www.mydomain.com. Since I'm confused by domain mapping, I saw a WP domain mapping plugin and downloaded it. When I went back to my dashboard to add the new plugin,it won't let me do anything - instead it sends me to a basic public webpage with the error message:
Sorry, the website http://www.mydomain.comwp-admin cannot be found.
This error message appears anytime I try to access themes, plugins, and other admin functions - but I can get to the dashboard, add posts and media.
I don't know where this is coming from. I didn't make any changes to my DNS file with my host or anything.
I really need step-by-step help. I'm super new at this, and not overly technical, so please be gentle ;-)