I've had this happen once or twice. First, I would try a hard reset (hold home and power button down until shutdown). If that doesn't work you should try a full restore. The Genius will likely ask if you tried this already and, if you did not, will do that very thing. If these steps do not cure your problem they may have other diagnostic tools to track down the issue or may do a swap for you. I think the latter is not likely as this is almost surely a software issue and not hardware related.