Can't access the admin controls…need help

What I did:

I went to the admin controls and logged in. Went to settings and then general and proceeded to edit the WordPress url and Site url. After doing so I clicked save and it brought up a very basic looking html type page with a white background and minimal text and my theme had dissapeared.

The only way to get rid of the changes was to click back on the browser revert the fields back to the original url. However everytime I do so, and click save, it takes me back to that generic white page.

What I was attempting to do:
The site is being used for a photography portfolio and the theme downloaded shows a large slideshow as the main page. After downloading the theme, the blog aspect of the site was set up as the main page rather than a standard link. I was trying to get the site directed to a different page rather than what was setup as the index.

Help is very much appreciated.