2007 Renegade start-up problem.

Hello everyone! 3 months ago I bought the ’07 Renegade. The machine seems to be in mint condition. Everything is fine, but last week when I was trying to start it up, I saw something’s wrong. When I turn the ignition on, the pump turns on without problems (the battery power is ok) but when I push the start button the starter doesn’t crank, and after 2 secs the pumps turns on again. It will start after 7 times, 15, or even immediately. (As I hold this button the lights shuts down totally, and when I let the button, they are turning on.) What it can be caused by? Please, tell me what to do 🙂