Help ZTE Avid Freezing in the night


Okay, so I go to bed pretty late, I don't stop using my phone until about 2 in the morning. But it works just fine. I keep it plugged in all night, even if it's charged already so that it doesn't die when I'm sleeping. But when I wake up, the light is green and the screen is black-expected, but then I'll push the lock button and nothing happens. Literally. The screen is stuck on black. This has happened two nights in a row, and the only thing I've done to fix it was take the battery out. This is a hassle, and I would at least like to know what is causing the problem. HELP.