Not starting after battery and starter replacement

Hello, need help identifying what could be my problem. My truck had been running just fine then one day it would not start up. Gave it a boost and it ran so I assumed it was a bad battery. Replaced battery and still had issue. When I would turn the key I hear a loud awful locked up grinding noise. Figured it was a bad starter. Got the car running by hitting the starter with a hammer and cycling the teeth with the key. The truck was working for one day and then just stopped. Would not start back up with the tricks. Bought a starter from AutoZone today and swapped it out but problem is still there. Checked fuses and wires. Not sure not what else. Fly wheel seems to be in good shape. Please help