Can you tell me how to fix a microwave when the start button will increment time but not start the unit?

SOURCE: microwave won't turn on

When you say that the microwave won't turn on, can I assume that you mean that the food does not heat up! If that is the case, the problem lies with the magnetron circuit. This circuit consists of the transformer, rectifier and the magnetron, the part that generates the microwaves to heat the food. If it is the magenetron, then it probally not worth fixing since the cost to purchase the magnetron is almost as much as a new oven. To diagnose if it is the magnetron that has failed, when you turn on the oven, do you hear a louder that normal hum or buzzing sound? If that is the case, then it means that the magnetron is shorted and needs to be replaced.

Hope this helps.