Why would my gasket blow without no warning of it over heating, only 67000miles on 2006 Scion xB

I didn't have any warning lights go on and Ive never had problems with it. One day I feel a loss of power( was going up hill) then big clouds of white smoke. Shouldn't there have been any signs? How much should the repairs cost?

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That mileage is really low, I've never seen problems with the ones we work on. Has it been diagnose for sure as being the fault? I wonder is the temperature warning light working properly or what component failed to cause the gasket to fail.
Yes I had it checked out, I did get an oil change 2 miles before it blew. The same place that changed the oil, worked on it for a few hour to figure out the problem. I know that the oil filter was loose , so I thought they were at fault. They spent a few hours on it and said # 1 & 2 gaskets were blown. How could this happen? They said no water was in the engine. They started it up and said it didn't start right away, but when I got in and started it there was no problem, and all the lights were off( cvs, ect.) I'm not sure where to go with this.