Start at the DB board: what a trip is actually telling you
A single MCB tripping repeatedly means one circuit is overloaded or has a faulty appliance or fixture on it. An RCD tripping means electricity is leaking to earth somewhere, classically through a failing water heater element, a washing machine, or moisture in an outdoor fitting. The whole board going dark while your neighbours still have power usually points to the main incomer or the utility's side of the connection, which is not something any private electrician is allowed to open.
There is one safe DIY step: unplug everything on the affected circuit, reset the breaker, and reintroduce appliances one at a time. If the breaker holds until a specific device goes back in, you have found your culprit. If it snaps back instantly with nothing plugged in, or you notice a burning smell or a breaker that feels warm, stop resetting it and book a professional. Repeatedly forcing a breaker that wants to trip is how melted DB buswork happens.