I've had this problem for a while and I think it was pre-jellybean as well. The whole time I've had my phone since July its only happened about 5 times. In this instances when I turn my screen off and try turning it back on, it won't respond at all. Power and home button are useless. In this last case, I had just turned on my phone less than 10 minutes ago so there wasn't any apps running except for Facebook which would eliminate a faulty app to my knowledge. I have an invisible shield so none of the sensors are being blocked. Has anyone else had this issue as well or know of a possible cause of this issue?