garage outlets stopped working
Your problem has all of the symptoms of a tripped or bad GFCI device. Insure that all GFCI's are reset. As far as diagnostics are concerned, at this point you will need a multimeter or ammmeter, or begin replacing parts helter skelter until you find or replace whatever is broken. 

First kill all power to the devices and lights. Then you need to open up all of the receptacle and light fixtures so you can access their terminals. Then you can turn the circuit back on and using your meter, you measure voltage from your source to your neutral and ground. It should be reading around 120V. When you find the devices that are not reading 120V trace back to the nearest intersection where you are reading 120V and not reading 120V, and somewhere in there is where you have an open circuit. 

I can say that before I started all of that, using my meter I would verify that there is 120V at the circuit breaker and then I would do everything I could to locate the GFCI. 

If your house was built after 1978 then your garage receptacles will be required to be on a GFCI device.

Good luck