Most (all) of today's new jets have a 'glass cockpit'. Everything is a small LCD screen. Some instruments are still analog, but eventually they are going the way of the dinosaur. A series of power failures can take the whole cockpit down.
That did happen in at least one case. I believe the 'Gimli Glider' was one of the worst incidents, and TACA flight 110 also. You really have to read about it to get a glimpse of how easy flying can turn into a really bad idea...
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The Gimli Glider incident was not exactly a "power failure". Yes, there was a failure of power, but it was due to the plane running out of fuel. It had nothing to do with an electronics failure, other than that the electronics, like the engines, which also failed, are ultimately powered by the jet fuel. An absence of fuel will cause a plane to stop functioning, regardless of the control system in use.
It's worth reading up about the Gimli Glider, not that this is on topic - an amazing series of blunders and accidents which led to a plane running out of fuel only halfway to its destination (the imperial to metric conversion for the fuel was done incorrectly multiple times, both before and after fuelling, both in Montréal and subsequently at its stop in Ottawa), followed by an amazing series of coincidences and strokes of good fortune (the pilot had significant experience as a glider pilot, the first officer knew the local area over which they were flying like the back of his hand having been stationed there as an RCAF pilot)... it's a great story, with a happy ending. http://en.wikipedia.org/wiki/Gimli_Glider