1998 Dodge Caravan, 96,000 miles, 3.3 liter engine

In the past couple of months, the key has been sticking (it can be inserted, but then can't be turned)After a few frustrating tries, it eventually turns and the engine starts and no further problems. It doesn't happen every time, perhaps once or twice a week. NOW-a bigger problem--the past two days when trying to start the van, the key will turn, but nothing happens. The engine does nothing-no sounds, no trying to turn over, nothing. After trying again, the engine will turn over and then start. There are no "wierd" sounds etc to speak of. This doesn't happen all the time either. We have cleaned the battery cables, but no improvement. Any ideas? HELP, please! =-)