Why won't my trailblazer start..???

Assumptions of components condition is a mistake. *HANDS-ON* TESTING MUST BE PERFORMED..

Thank you for your very helpful advice. But like I said before, the battery is good. That was the first thing I made sure of.. also the alternator and starter check out. Changed out the ignition switch for nothing also... Checked grounds and cables.. now what?

Thing that’s odd here is the fact jumper cables actually made a difference.. That’s indicative of a shorted / defective battery that must be load tested with proper tester and should have specific gravity tested using a battery hydrometer. Good luck with it!

Your statement: “Jumped started worked but when turned off and it won't start again”