engine won't crank over on 2002 Chevrolet Trailblazer

tried to start car turn key engine won't crankover battery is good i changed starter relay still won't crank over

Asked by for the 2002 Chevrolet Trailblazer
How about the ignition switch has that been checked? you can put a meter down at the starter so when the key is turned to the crank position power should show on the meter