Check the fuses.If not the fuse, test the resistor down by the blower motor.
its your blower motor
the blower fan resistor has gone bad.
blower motor resistor is burned out
Defective Blower Motor Resistor Pack.
Loose connection or blower motor? Bad blower motor? Loose fuse? Bad fan switch?
you need a new blower motor resistor
Possibly some leaves have entered through the fresh air intake.
The heater blower switch and the electrical plug attached to it may be at fault. Remove the heater control unit from the dash and inspect the plastic electrical plug attached to the blower switch, you may see it has melted. The switch and plug is available from your local auto parts store.
Blower motor, resistor, wiring or control problem are common causes
There are probably over 100 potential reasons why they're not working. What the actual reason is... more information would be needed to determine this. For starters, the symptoms. It could be as simple as the blower not working, or it could be something much more complex.
Probably the blower motor speed resistor is partially burned out.
What kind of car is is it? Without knowing anything else, I would suggest checking the fuses and relays. It should be the same blower; does it work with the heater? If so, it could be an issue with the a/c - heater control in your dashboard. It could also be a bad blower. If you can get to it, you can check to see if there is current going to the blower with a mulitester. If there is, and it's not on you know it needs replaced.