First thing I would suggest (if you haven't done it already), is a simple reboot. After that, booting in safe mode will prevent any user installed applications from interfering with the operating system and thereby eliminating the possibility that they are the cause. If in fact the problem still continues once you've done that then it's a problem with the operating system or hardware failure. The next step after that then would be to do a full factory data restore, and if that doesn't fix the problem then you have a hardware failure.