Start with the highest range to see if you get a reading, then drop down a range, etc. Software doesn't work intermittently; it may be starting at the highest range, not "seeing" anything and therefore doesn't drop down to the next range. Whatever is switching between ranges, small relays, solid state switch, is causing the problem. My bet is on a bad "switch" or a cold solder joint. I had the same thing happen to me on a process meter and found several cold joints on one of the surface mount chips. Repaired and back in business.