Site Disappears From Google After Theme Change?

[David]

I've got someone who uses wordpress for their site and they were listed on Google before they changed their wordpress theme. After the theme change they now don't show up for their keyword but more importantly if you type in their domain in to google they are nowhere to be seen anymore.

Does anyone know why this might of happened and how to rectify it?

Thanks
The "Discourage search engines from indexing this site" box remains unchecked in wordpress.

[J]

did they select "do not index" in the new theme options panel?