Multiple Echo Dots - one not responding vocally

[Cheewawas]

I purchased three echo dots a few weeks ago.  The first one I set up has quit responding vocally.  Her little lights buzz around but I get no audio response.  Has anyone else had this problem?  Can Individual Dots perform INDIVIDUAL tasks at the same time? (in different rooms, of course)

[Cheewawas]

lease disregard my question.  By process of elimination....unplugging two devices, I was able to see which one was on-line and getting the Serial No. for it, then I sequentially plugged in the other two for the same info.  I've labeled the bottoms of the Dots with their respective serial numbers.  Could have been easier if the number had already been on the device itself     Still working on the audio of the one that's no longer talking back to me.