Site is down - not sure what to do next

Hi, my website, http://www.ocdiscountmattress.com is seemingly down. the homepage comes up, but none of the other pages come up. I can't even access the wp-admin page. The only thing I have recently changed or added to the site are some WPMUDEV plugins, nit that I necessarily think they are the issue, because the issue started days after any changes were made. Not sure if this is something that you can help with, but I have called GoDaddy, and they can't seem to help in any way... Thanks

Gates