I had this issue after I had rebooted it a few times. I saw that the Hardware Version was blank. I updated to the latest firmware and now its working. I hope this helps.
where did you download the latest firmware from? I tried downloading from their site
https://shop.bitmain.com/support.htm?pid=00720161126080548570Q2tDBXAH065D but it seems their amazon web services is down :/
thanks