Well i used to have a 4 speed fan and now its like all the others with the 1 & 2 dead and three and four working very well however with a twist....

Now when i go to put it onto speed three and above it actually turns the air cond off - it still works on one and two but i could fart through a table better than that pushes air out and if i put it on three or above it just pushes out the existing cold air in there and then blows non cold air out if you know what i mean - how is this fixed and how did it happen?

change the fan speed resistor

As magnus said, change the fan speed resistor, it is in the fanbox up under the govebox.

how did it happen?
How does it work?
With the fan switch in the number 1 position, the V+ to the fan should go from the switch and through the resistor coils for all 3 slower fan positions then to the fan,
with the fan switch in the number 2 position, the switch is simply wired to a terminal that bypasses the 1st resistor coil (so power now only flows through 2 resistors and a bit more gets to the fan making it run faster)
With the fan switch in the 3rd position, the switch is wired to bypass the 1st and 2nd resistor coils (now only 1 resistor and more power again to the fan)
in the fastest position there are no resistors, the 12V+ is supplied directly to the fan side of the resistor block and so straight to the fan motor.

The power for the A/C switch is controlled by the fan switch
i.e A/C won't work with the fan off.
To do this the a/c master switch gets it's 12v+ from the curcuit between the resistor block and fan switch 1st position, if the fan resistor is in good condition and the fan is set to a faster speed then the A/C switch will still be supplied a voltage back through the resistors
but if a resistor coil is burnt out then the fan won't get power at speeds below the fault and the A/C won't get power at speeds above the fault and so the a/c and fan won't run together.
(As the fan speed is increased the voltage to the a/c switch is decreased by the extra resistors, the a/c master switch will only get 12v when the fan switch is in the 1st position)

To get the fault you describe, I bet the fan resistor is blown at the no2 resistor coil, as suggested replace the unit.