DAC sound going out

Been testing DACs in a computer setup lately - Audioengine, microStreamer, Dragonfly - and just got a Micromega MyDac to try. I got it up and running, but then soon the way there's a crack (speakers) and the sound goes out. The MyDac lights blink to indicate no connection. Unplug/replug USB and power to DAC, maybe reboot, check Sound settings (Win 8x64), then USB light is on and audio returns. That happened twice awhile apart earlier today. Once was during an mp3 file playing (big band at moderate volume), later when I closed a webpage. This afternoon I left the DAC running with the speakers off for burnin. Came back a few hours later and found no sound, and so far can't get it back. Plug in Dragonfly, which of course gets power via USB, and sound is fine. Anyone run into something like this?

With the other three DACS, I also get a pop occasionally closing a webpage, but it's mild and the Audioengine tech told me that pops are common with these type of DAC setups. Still, I had to wonder about a spike. I use one of those old computer consoles, with the computer, monitor, two Emotiva airmotiv 4 speakers, and now the DAC plugged in. Except for the MyDAC and monitor, power cables are a Pangea 14 and two MAC HCs. The printers are off on another surge protector, but the whole (bed)room is on one fuse in the breaker box. Ideas what might be going on welcome. Thanks,
Correction: that third time, when I couldn't get the sound restarted, turned out to be because either the front input knob or USB 1.0/2.0 switch or both had changed positions. From a technical standpoint, from grossly inadequate install instructions to fickle knobs and switches, Micromega has made the MyDac a real PITA to use (reading reviews of similar designs, these sorts or problems seem to be common, e.g., iFi DAC). In any case, at low-moderate volume, it made it through the night w/o losing audio.
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