'97 Will Not Start Until Fan Stops Running

I have recently purchased a '97 Taurus LX that is having a strange problem. When the key is first turned ON the engine fan starts to run for a few seconds and if I try to start the engine all it will do is turn-over and not fire, once the engine fan stops after a few seconds(between 5 - 45 seconds) it will start nicely. Anyone know what the trouble could be? Many Thanks,
Steve