HD510 fails to start up - stuck at "Continue"

[Peaspod]

HD510 is failing to complete the startup. It gets to the first "Continue" screen on the LED screen, button beeps and depresses, but nothing happens. Controller is showing green light. I've tested all the plugs, and they appear to be seated correctly. The startup worked fine about a week ago when I last tried it, so this is new behavior. Any clues on steps to take to try to resolve this??

[Peaspod]

2 successive Pendant calibrations resolved the issue.