1999 Other Chevrolet Models Truck wont start

I have 1989 chevy s10 blazer with 200 thousand + MILES. Sat I drove for about 45 min just like normal no problems then I was at a stop sign and it all of a suddon died. Never would start. Turns over like she wants to start just wont. I listened and I can hear the fuel pump come on, and couldnt figure it out. So I left it over night. Went back sunday and battery was compleatly dead. Got a boost still wouldnt start. Just turned over but never started. Took cables off and dead. Could this be my altinator? I dont know a whole lot about cars, andy help would be great thanks