What "unit" did you replace?
Which "breaker" trips? Overload or earth leakage?
When you "switch the power on"..... to what? Something that is plugged in? Do you mean when you reset "the breaker" with nothing plugged in?
Does "the breaker" trip when there is nothing plugged in anywhere? If not, plug stuff back in one item at a time and suspect any item that causes a trip.
If you find an item that causes a trip, see if it causes a trip in another socket.
Overall, it would be far, far safer to ask someone **competent** to look.