Total loss of power is rare. However, believe me, I have attended many callouts to address complete black-out situations.
Total loss of power can be caused by both external and internal electrical faults.
Possible causes of a total power outage:
If you have an RCD (residual current device) as the main switch, it may have tripped. If you don’t know what an RCD is, look at Image 3 and Image 4 below.
You may have a loose connection somewhere between the fuseboard and the main service head.