This is what happens when you turn off your UPS.  Never turn off a UPS in critical applications. That’s why a UPS was put on your system in the first place to make sure that the power doesn’t go off!

http://www.independent.co.uk/news/business/news/british-airways-system-outage-it-worker-power-supply-switch-off-accident-flights-delayed-cancelled-a7768581.html