Maybe the coolant temperature sensour went "Bad" ?
EDIT: Opps ! You didnt mean the radiator fan... you really meant the "blower motor" ?
If its the blower motor itself you could try replacing it with a new one... or you could try giving your older blower motor 12 volts, and see if it spins when voltage is applied directly to the terminals. My GUESS is the motor has likely seized up...
2nd EDIT: Many blower motors use a series of resisters along with the fan switch positions so that depending on the switch setting the fan blows at low, medium, medium high, or high speeds. Sometimes the blower motor itself maybe fine, but if the resisters melt down and no longer conduct electricity, then no mater what the switch setting, the blower motor, if it isnt getting any voltage, wont be blowing any air through the ventilation system. In this situation, maybe it might make sense to replace the burnt out resistors.