An air conditioner blower that won't come on is normally caused by a problem with the thermostat, breakers, micro-switches or the blower motor itself. Sometimes the evaporator or condenser may be clogged with dirt or other debris.
Check the breakers to see if they are all in the correct position. Also, make sure the access doors to the blower are closed. Micro-switches in the access doors prevent the blower from starting when the door is open or even slightly ajar. Test the thermostat by turning off the heating and air conditioning and sliding the blower switch to on. If the blower comes on at this point, the thermostat is likely the problem. Also, check the evaporator and condenser for any clogging. When the blower motor itself is the problem, it is best to call an electrician.