Theme not appearing

Hi I am currently trying to add a theme to my client’s website. Their current website was programmed by them but they decided to move to www.ads-software.com. I have activated the biz-growth theme but when I go to customize it the screen is blank and I am totally confused! The site is still under their original programmed theme so I am wondering do I need to launch the theme site in order to see it? Any help would be appreciated!