Last week, it was discovered that setting your iOS device system date and time back to January 1st 1970 would crash your iPhone, iPad or iPod touch effectively “bricking” it (though why you would do this is beyond me). Setting the date back this far would prevent the iPhone or other iOS device from booting up until the battery died.
A bricked phone means that it won't turn on no matter what you try. In other words, it’s as useful as a brick for making phone calls
Apple has acknowledged the problem and says An upcoming software update will prevent this issue from affecting iOS devices. If you have this issue, contact Apple Support.