Its very hard to say without knowing if there is a healthy electrical supply at the fan when the light switch is turned on. Its a process of elimination starting with the most obvious.
01 - Is there a fan Isolation switch
02 - How old is the fan
03 - Does the fan have humidity/timer/overun
04 - Has any work been done recently
05 - Does the fan start or show signs of working (motor sticking)
Matt, January 2009
