Replaced battery cannot get the car to stay running

My car was slow to start over a couple three days I went to O'Reilly's they tested my battery I had a dead cell. We replace the battery check the battery I was not getting a charge to the battery. Went home to replace the alternator took the alternator back to the shop they tested my old one it was still good. I put it back in I tried to start the car for a few seconds and shut off. I understand I may have to reset the alarm system what should I do? I cannot get the car to keep running.