It appears some iPhone 5 users are having some major problems with the latest handset from Apple. The power button isn’t exactly turning on and off the way it should.
According to iPhone Touch, the iPhone 5’s power button sticks or doesn’t properly depress the way it should. This results in users having to press the power button at an odd angle in order to get it working properly.
While there doesn’t seem to be an official fix for the problem or a do-it-yourself solution, the best advice is that under the warranty it’s probably prudent to return the iPhone 5 and have it replaced, as the problem is reportedly a mechanical issue and not an cosmetic one.