My '97 Chevy Malibu 3.1 L 6 cylinder is having problems?

One day my car just died, when I got it home I tried to start it and it took a few seconds while it slowly cranked into life and when it got cranked into life it would die after few seconds of running it, the engine would start to get slower until it finally conked out, and also while it was running it sounded rough, almost sounded like one of the spark plugs wasn't firing and after trying to figure out what it was wrong with it the starter died, i would try to start it and when I turned the key the belt in the engine would move a little bit and it would stop and like when you start a car and the engine chugs well it just chugged once and died, also some car history it has 150K miles on it and I just recently replaced the power steering pump which means I had to take of the serpentine belt to replace it, and also while I was driving it before it died at certain times it felt like it got no power like all the acceleration had disappeared, could it have been the starter causing this problem or could it be the alternator or both, I tried changing the cam sensor and it did nothing but I did not try replacing the crankshaft sensor any and all ideas would be helpful but do not tell me to ask autozone because the one I went to told me that it was the cam sensor that was at fault but found out it wasn't, and after that they had no ideas.