Submit Buttons don't work..

Hi there. Hopefully this hasn't been asked and answered, I've been searching all day.. For some reason none of the plug-in's that incorporate a "submit" button work on my new site and I don't know what to do. I've tried a number of options, including the contact widget and they all have the same results. They look perfect, but the buttons to submit do not do anything. I haven't installed anything that I'm aware of outside the WPMUDEV plugins, although I do currently have a contact form from a third party on there to test and got the same results.

Has anyone seen this before? I'm totally at a loss.

Thank you so much in advance for any assistance / advice you can provide. It's greatly appreciated.