If you are sure the battery is good and fully charged and the cable connections are all good. You will need to check for voltage at the small purple wire on the starter solenoid while some one engages the starter. If you have good voltage at the purple wire and at the large battery terminal both, you will need to replace the starter. If you do not have voltage at the purple wire let me know so we can test the starting system and find where the problem is. But be sure to check to see if you have any theft or security lights are coming on, on the dash first. It may be an issue with the security system also. Thanks, Bob
Auto Service Technician
40 year GM Tech. +30 Certified. ASE Master Tech.(expired, retired) Medium Duty, Heavy Line, Retired