How bad was the crash? The gyros are pretty sensitive and delicate on the inside. A great enough shock can put them out of service, by either damaging the sensor, or overloading the electronics within.
Some are equipped with overload protection, which usually gives a visual or audible indication that OL has occurred. The process to reset those probably differs with each manufacturer though.
As for your 3gx, see if the manual has a section for Errors.