The first thing I'd do is grab Akeeba and back that baby up before you do anything else. This could get messy or it could be an easy fix. It depends on how patient you are.
I see one potential problem, but I don't think that's it. I believe you need to check your PHP version, although if other Gantry templates are working, I don't see why this one wouldn't.
You've gotten your Gantry installation skewed.
You'll need to go in an manually remove the Gantry files from your site. Then, reinstall. I'm pulling together some info to guide you on that.