"Can't find server"

I’ve just recently taken over managing a WordPress website for a church. I’m still learning it; meanwhile, the site has apparently gone offline. When I try to go to the site itself or the login page, it says, “cannot open the page because…cannot find the server.” No one else is able to access it either. I was just going to contact the host, but I don’t know who that is and neither do the people I work for. That was all handled by the previous web manager and he can’t be reached. What can I do to fix this myself ASAP??