2000 grand voyager

The other day I went to start my van and it wouldnt start. It turned over ok but it would not fire. I set up an appointment to take it in the shop for the next day. When I was going to take it in I tried starting it again and It started right up. It ran great for about 3 days and now its not starting again. It has spark and I hear the fuel pump coming on. Any Ideas??