When I first bought my phone the screen would go black. This isn't the normal phone-going-to-sleep, but more so the screen would go black, but I could still touch icons and stuff (it'd make a noise), receive texts, etc... I just couldn't see anything unless I restarted my phone.
The fix for this, at least for me so far, has been to remove the battery for an hour or two and put it back in.
The fix for this, at least for me so far, has been to remove the battery for an hour or two and put it back in.