On MSNBC's countdown to Doomsday, one of the ways that paricularly creeped me out where the following.
A huge solar flare erupts from the sun, creating a beautiful aurora, but unfortanetly rendering satelites useless, and hitting the U.S. with a strong particle storm, knocking out electricity in one region of the U.S., preventing electricity from flowing through there, causing an overload burnout chain reaction, that causes all of the United States and Canada to lose electricity, rendering the pwoer grid completely useless in need of being rebuilt.
At first none of us know what happened, because there is no way to communicate. Within days all of the nations food supply spoils, without refrigeration. The shelves get empty at the stores, and there is no way to order more, because gas is running out because the pumps don't work. Without any government or law enforcement, coupled by strong hunger people start to panick. There is mass looting, chaos, and criminal activity. No way to call for help.
The factories we would normally use to get the power grid back up and running, are also useless because they are without power.
And it would take a minimal of a year to get the power grid back, but by then most of us would starve to death. The U.S. economy would be hit so hard, there is no coming back from something like that. Just starting over again.