Blower was working fine ,come and cut off. Blower fan came on with no heat or air on and didn't cut off, had to unplug blower fan to cut it off. What wrong?

The blower came on with no call for either heat or cooling? Make sure the thermostat fan setting is set to 'auto', not 'on'. If all is well there, disconnect the wire from the "G" terminal on the furnace control board to see if the fan stays on.