1qaz

I am a R/C scale airplane guy since the 70's and my wife wanted a drone. We bought the Dromida Vista at our local hobby shop, flew it for 2 short flights during which it seemed to work fine. Now back from the flying field my wife took it out in our back yard and one of the two front motors will not start. What is really strange is that the problem seems to switch from left to right on the front set of motors which makes me think it can't be a motor issue. We tried new batteries in the TX, re-calibrated the thing several times and still nothing.
Any ideas? Being new to the drone world maybe its something simple that we are missing?