I've had the phone for two weeks now, and i just encountered this problem this morning for the 1st time.
I left the phone on my desk for a while. And when i returned, the phone was completely blacked out. I tried to power it off or on, but it didn't work. My last resolution was to take the battery-out and put it back in - which then worked.
Then, this afternoon again, my phone was locked after a while, then, when i returned to the phone, the notification bar on top of the screen (where it shows power status, time, etc....the bar was completely clear with no image. And my background wallpaper was completely black. When i tried to enter the patter to unlock the phone, it didn't respond. So, i had to use the power button to turn off and on.
I just transferred some media (picture) files on to my SD card last night. And that's pretty much the only change that was made to my phone since.
Has anyone had this problem?? Is this a known issue??? or is it a phone defects?