I just came back from work. I was rendering this scene again with Ryan's suggestions. I think I need more memory, the computer was frozen up. The event log said 'stack overflow' and that the swap file size was exceeded. I was rendering at 1680 x 1008, detail 0.9, GI detail 2, GI samples 4, AA 7, using one thread. I have 2 gigs of ram...
Windows Defender had an update. It usually does a scan right after updating. (Annoying program!) Maybe Defender had something to do with it?...