Car wont start iM stuck please help

Ok I just bought a 2003 ford Taurus from a family member. She kept very good care of it and I got it for a great price. Well I had the car for a week and replaced the starter the altinator the battery and the ac compressor froze up so I bypassed the pully. Worked great for about 2 weeks. Wendsday I drove to work just fine 6am. When I got off 3.30pm my car started fine but squealed louder then any car ive heard me begin embarrassed I drove off a short distance down the road I pulled over popped the hood turned the ignition off abd took the key out the car was still running but at a very low idle and still squealing. I saw no problems so closed the hood and put the key back in and turned to on. The car jumped up to normal idle and stoped squealing. Thinking it was ok I drove about 30min to Wal-Mart drove great. When I got back to the car it wont start. Turn ignition to on all lights work all power works, try to start it and nothing no click clank clunk nothing the motor doesnt even turn over. Tested the battery, altinator, look at serpintine belt tension everything good. So I thought ok maybe starter. I jumped the starter off my battery it spins fas. And free but still wouldn't turn motor. Any ideas please my kids start school in 1 week and im about to be fired please someone have a answer