There are many reasons why a Sportster might not start. Perhaps the battery is chemistry isn't correct, or the starter motor needs to be re-booted. Perhaps there's a dead battery somewhere in the system. Or perhaps something else is wrong with the bike that needs attention.
The best way to diagnose and fix any issue is to gather all of the information you can about what's happening when your bike won't start, check for related symptoms in other areas of the bike, and try to DIY if possible before taking it into a shop.