1 Site within a Multisite is not responding

I have a multisite install made up of 8 sites; 3 are live and 5 are not. I've mapped all of the sites using the WPMU domain mapping plugin but only one is not properly receiving the domain mapped traffic while the others are fine. All of the sites are mapped the same way.

I can log into the admin side of the problem site within the multisite environment, but the page load on this site's admin is super slow compared to the other sites.

This one problem site isn't finished, so I need to run the Coming Soon Pro plugin to post a custom holding page. I can't even get the plugin's Live Preview page to render.

I desperately need someone to log in to the admin account to see why this isn't working.