2000 Jimmy - starts but can't shift into gear - can't push button in

Check ALL the fuses !!! Does the brake lights work? if not,, the shift inter lock may be disabled ,,, if the lights work the interlock solenoid might be the culprit . You should be able to get in gear by turning the ignition switch off then turning to the first selection ,,don't turn it untill the dash lights come on ,,with the key in that position you should be able to shift the lever to put it in gear ,,,,dont move the key untill its in the correct gear