1989 Ford Aerostar won't shift

When I drove my van home from work (approximately 15 miles) it seemed to be running and shifting fine. As I turned to go up my road it didn't want to shift into second gear, after stopping and letting it sit for a few seconds I tried again, no luck. Then after about the third attempt it wouldn't even go into first, or reverse. It won't budge. I have not had any previous problems for the most part it's been running fine for a 20yr old vehicle. I don't have a lot to put into the vehicle, any suggestions?