Sometimes my screen seems to short out, the phone is still on and

My phone screen will turn completely black (as if it was locked) and no matter what I try, it won't respond to anything short of me taking the battery out and placing it back. The phone is still on because the apps are still running (music) and I can see a VERY faint screen, however it won't restart or illuminate when I try the power/unlock button. It has happened at various times under various circumstances.