Hi
The "main breaker" generally refers to the 120V side of things. Depending on just which entertainment system you have, it may run on
12V rather than 120V. If so, the things to check are more on the 12 V side of things (converter / charger / battery / ...).
If it *is* a 120V powered unit, it may be fired. Simple answer there is to unplug it and run it to a known working outlet. If it still does not fire up, that may be related to the question "why did the breaker trip?" .....
Bob