My doorbell is lit but it won't ring, what do I do?

Knock on the door? Sorry,couldn't resist.

Here is a link I think you may find useful.

Repairing a Door Chime or Doorbell - The Home Improvement Web Directory

We have an intercom system (which includes the doorbell). When it storms or there is lightning, it ceases to work. I just trip the circuit breaker and it works.