I posted on this elsewhere, but I'll summarize it again.
I am not sure if it the same situation, but my phone's screen would randomly go black, sometimes for hours at a time. The notifications would still go off, I could hear incoming calls ring, but could get no access. I would try to turn it off, but the green notification light would just keep blinking. I would pull the batter, and try a restart, and could hear the sounds of the phone restarting, but still the blank screen.
Sometimes after an hour, the worst time being 8 hours, the screen would come back. To make a long story short, I had to have the phone replaced. They tried wiping my phone clean, and doing a hard reset or something like that, but it did not help. Also worth noting, this did not start happening until months after I purchased my phone.