Car won't start

I have a 1992 Pontiac Grand Prix 6 cyl 3.1 engine, 85,931 mileage. Last night I was going to the store and I was coasting down the hill, stepped on the gas and nothing happened, as if I wasn't even touching the pedal. It was like that for about 5 seconds, then I got gas, pulled into the parking lot, then pulled into a spot when it died. It's been dying more than enough times lately, after the mechanic "fixed" the car. I never had problems before he worked on it. Anyways, I started the car, it started right up nicely everytime, but would die. I was there for over an hour letting it sit then trying again. Usually if I let it sit for a few minutes it would start no problem, but not this time. I ended up leaving the car there til this morning. I even went and bought new jumper cables. The headlights, interior lights, radio all work, but the car still won't start. And here's the kicker. The clamps connected to my car never sparked. We put in a brand new alternator a couple weeks ago so I know it's not that. Could this simply be a wire in the battery loose? I can't recall for sure but I believe we bought a new battery in August. And if it is a loose wire, could you tell me what to look for the fix it? Thank you in advance.