2001 Dodge Caravan Car won't budge.

Went to accelerate when the light turned green. Van bumped or jerked about three times and then stopped. Would not go, but it sounds like and feels like it is trying. We were able to push it off the side of the road, but then it locked up completely. We can not push it or make the wheeles move wether it is in nuetral, drive, or reverse. Any ideas as to what is wrong?

Thanks.