why dose fan not work?

If the fan is rotating but air is not being extracted then there's a problem with the airway - blocked or fallen apart - one or the other.

If the fan is not rotating then there's either a problem with the fan itself (broken) or a problem with the power supply - fuse - wire - switch - control board perhaps.

Nobody here can diagnose the precise reason with any accuracy - you will need to do that yourself or call in somebody to help you - neighbour or specialist engineer.

It often helps to say the make and model of the appliance and in this case if the fan is actually turning as it should - can you hear it or not?

Good luck...

S Hawking
September 2014