I have a insinkerator pro 17 disposal, it works but once I shut it off it won't turn back on , it just humms. I press the red re-set button if necessary but it usually doesn't need to be re-set. I have to keep loosening the hex bolt underneath to make it turn on but the same problem occurs once it is shut off

The pro series have a batch switch in the collar. Bad idea in my opinion. If the unit can be freed by using the hex wrench and then jams again, you either have an object caught in the grinder or a bad bearing. Try this, fill the sink with water, free the disposal get it running and then let the water out. Hopefully it will free up anything caught in the grinder. If you replace the unit Badger series are less troublesome.

Where is that batch switch? What is the collar?
I don't have the specs for the Pro-Series Insinkerator 17

where is that batch switch? What is the collar?
I don't have the specs for the Pro-Series Insinkerator 17

Where you insert the top to turn it on. Google your model for a manual and info.