Circuit breaker for garage
There may be something on that breaker's circuit that is causing it to trip and prevent a fire/short. 

What you need to do is find everything that is on that circuit. Afterwards, see if there's anything in any of those objects that could be tripping it. Connections becoming overloaded, being loose or wired improperly could also cause it to trip. Be sure to check that as well.

If you do find something, resolve the issue and reset your breaker.

However, breakers may trip by themselves from old age at times. If it wasn't caused by anything else I mentioned earlier, this may be the cause. You'll need to replace that breaker. If you're not sure how, I recommend you hire a licensed electrician.