This unfortunately seems to be happening to me as well on the AC3100... after a few days, the GUI becomes unresponsive. The first time in, it does ask for a username/password, but then after it times out, and after many retries, it's just a spinning browser. All other functions seem to be working OK, however I do have to agree that it does not seem to reboot automatically on its schedule at times. Good ol' manual reboot fixes it for a short while. This problem was getting so bad, that I just decided to set it to reboot every other day at 3am... sometimes it does, other times it doesn't... and usually when it doesn't, I can't get back into the GUI either. I'm going to give that ssh command a try, and see if that works for me (service restart_httpd).