I activated a new theme for my site and now my site isn't appearing.

I am the webmaster for an online directory website called http://www.bergenline411.com . Earlier today I purchased a new directory theme to replace my current theme. I just uploaded the new theme’s zip file and it was successfully installed. BUT when I went to go activate the new theme, I lost EVERYTHING! I even lost the wordpress dashboard for the site. All that appears is a white screen no matter what I click so even if I wanted to return to the old theme it won’t let me.