1999 XJ electric fan won't cut off, car won't idle

My friend has a 1999 XJ with the 4.0, and when she came back today her battery was dead. I went to help her jump it off and heard the fan running. The car wasn't on, and the keys weren't in it. The fan was running constantly all day which killed the battery. I jumped her off and went to start it and the car won't idle. It runs great, and ended up driving it home, but it won't idle at all. It cuts off. What does this sound like? Thanks!