This has happened to me twice in the space of a couple of years & is REALLY ANNOYING! The first time after, about 3 days, it just reset itself! The second time I did everything that people recommended like holding down the volume button whilst pressing the on key at the same time. I did this with the phone plugged in, I did it without the phone plugged in, for anything up to 20 seconds but nothing worked!!! I had reached the point of thinking I would have to send it for repair when, suddenly, the screen went blank. I plugged it in to charge it up and, hallelujah, the screen was unfrozen and it charged up!!! Most frustrating however being unable to use it for over a week!!! It seems to me that on both occasions this has happened my phone has been almost out of battery. I wonder whether this has something to do with it? Just in case I suggest you keep your mobile charged up at all times (I am certainly going to do so). I really don't know whether this is the answer but I put it out there and hope it helps. My only other suggestion is to wait & it might just reset itself.....eventually!!!