The window will not always go up, only sometimes. what could the problem be??

Check your wireing that goes from the vehical to the door,it will break wires in that harness over a period of time.

I had the same problem with my 2002 safari. It first did it on the driver's side window and then later on the passenger door.
This is a known flaw with this vehicle. It has to do with the solenoid overheating. Once it cools off it will work again. Phone up your dealer and talk to the service dept. They will be able to tell you the exact part and what to do.
Lucky for me it was (just barely) under warranty when it happened on the first window and for the second we knew what the problem was so just bought the part and fixed it ourselves.