1992 Buick Roadmaster

Engine Performance problem
1992 Buick Roadmaster Two Wheel Drive Automatic 135000 miles

my roadmaster will not start, I had this problem once before and I replaced the battery that was two days ago. It worked fine and then later that night after replacing the battery it started cutting off in reverse so I replaced the plugs and wires. I drove to the store after replacing the plugs and wires and the car would not start again. Could this be the starter or the altenator or does it sound more like something else? Just bought the car and already have 2500 into between the purchase and repairs need to know what I am getting myself into