1992 Pontiac Grand Prix won't start

My car was fine early this afternoon, but 2 hrs later when I tried to start it- it wouldn't even try to turn over. It beeped like normal & the lights & radio came on, but its like it wasn't catching. We tried jumping the car, my husband tightened everything, checked the fuses. Nothing! I don't know if the 2 are related to this or not, but it has been stalling now & then. Also, mostly on the highway, the car shakes. At first it was just a little, but lately you have to hold the steering wheel pretty tightly. We assumed it was a broken belt in the tire & planned on getting new 1s this coming weekend. HELP ! Does it sound like the starter? Or the computer?