Verizon/HTC Thunderbolt: I will turn screen on but my screensaver is gone and the screen will not unlock. The screen is black w/the clock showing the time it froze. The standard icons are present as is the half circle I use to unlock screen. When frozen, I cannot turn it off w/the power button. I have to take the battery out. I don't know why it's happening or what I can do to prevent it. Any suggestion will be greatly appreciated! Thank you! Side note: it's not live wallpaper, just a standard HTC offering that came w/an update. The freezing is happening more frequently these days. Any ideas???