Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power for the entire

Monday's still-unexplained power outage was the most severe ever to hit Spain and Portugal, which have a combined population of around 60 million people.

The hunt has begun for the cause of a massive blackout across Spain, Portugal and parts of France that halted trains, bank machines and traffic lights, in one of Europe's biggest ever power system collapses.