DIAGNOSIS
The device is stuck in its camera tracking or 'Motion' mode. The microphones are likely muted, indicated by the red light ring.
FIX
First, check the microphone status. Say "Alexa" or look for a red light on the top of the device. If the light is red, press the microphone on/off button on the top to turn the microphones back on. The device will say "Microphones on" and the spinning should stop.
IF THAT DIDN'T WORK
Perform a hard reset. Press and hold the Action button (the button with a dot and a circle) for 25 seconds. The screen will turn off and the device will reboot. This clears temporary software glitches.
HEADS UP
Constant spinning with a red light means Alexa cannot hear you. The motion feature is independent of voice control. Ensure the microphones are not disabled in the Alexa app under Device Settings > Microphone.