89 Voyager won't start

1989 Plymouth Voyager with 3.0 liter V-6. 130,000 miles on it. Gets very infrequent driving these days, but it was driven Friday and Saturday with absolutely no problems. Then Monday morning it would not start. The engine will grind and grind but it won't turn over. Battery is strong. I seem to have a spark. I'm just wondering what else I can check myself before having the thing towed. Any at-home troubleshooting or other suggestions appreciated.