The alternator light came on and a week later it died?

I had my truck for a while and the alternator light came on and a week later it died so I got a new alternator and a new battery and it turn on but the check engine light was on and the alternator light was on and then a hour later it turn off so I replaced the battery and alternator again and it happen again I dont know what could be the problem please help me its my only vehicle and everyone I talk to has no reason why its not turning on and this is my last chance