The Alleggro A3977 chips used on those boards have a max operating voltage of 35V, above that they may experience various internal breakdown effects, however whether they are damaging or not depends on whether they were current/temperature limited. It is likely, but not guaranteed, that they would survive 42v in standby mode but back emf from the motors (if they ran) might produce high energy spikes that could be damaging.


I suspect the power LEDs are taken off the 5v rail which is regulated off the 24v rail. It may be that the regulator is overheating at the higher input voltage and going into shutdown. Measure the 5v rail voltage at the output of the regulator (the L7805 3-legged beast)