I ran into this problem after I installed W3 Total Cache plugin. After a lot of trial and error I found that when I disable the cache of the Front, or home page, that the site would display fine in a browser. My Front/Home page has a slider slide show on it, so perhaps that combined with a cached version of the page had trouble loading...can't say. But you could give this a try.
It's worth figuring out as the W3 Total cache does allow for caching o Error 404 pages which I found dropped a lot of CPU load as spam bots tried to link to old deleted Comment, Activity, or Group pages.
The path to the setting is;
'Performance/Page Cache/General/. UN-check 'Cache Front Page'.