If your overclock is too high the hash board will crash and give you a 0 reading, just go into the overclock settings and lower the setting and hit apply and the miner will restart with the new settings. Some people will start at 650 and go up step by step until it crashes. Keep in mind that when ever you get close to the sweet spot it might still crash. For instance mine will run at 675 for about 6 hours then one of the boards crashes. At 668 it will run for 12 hours and crash. Best setting for mine is 662 and has been running stable for 6 days with out any problems. I have a batch 2.

hope this helps.