I have a Makita plunge router mod.# 3612C. I do not use it a lot. I was using it and it quit running. There is power to the switch and going out of the switch.

Check to see if you have power to the brushes on the motor, if you DO, then most likely the brushes are faulty, if NOT then you have some sort of disconnection between the switch, and the wire, also measure from the "Other" side of the motor, and see if it returns to the Neutral.
Basically, the power Phase, comes into the "Hot: side of the On/Off switch, a wire goes from the cold side of that switch, to the Hot side of the Motor's brushes. The Other Motor terminal, From that Brush, it will then go to the Neutral, return wire.
Also sometimes, If it quit running, mid job, as it were, then I would suspect, a Wire has broken or a Brush has broken etc. There is also a thermal fuse berried inside the motor this too can fail, but only usually from overheating and most often it will "reset" when cooled. Check the actual On/Off switch itself too, I have had them go open circuit before today.