Originally Posted by 8mileroad
Stock ROM not rooted. No modifications what-so-ever.
Try doing a factory reset. Sometimes an app installed on the phone might screw up with a hardware's function. For example, I've always use Screebl Pro on my phone to let it control how my screen turns off. I decided to try their new Beta version. A few days later, I cannot seem to manually turn off my screen by pressing the power button. Every time I press the power button, the screen will come back on on its own. I can try up to 4-5 times before it eventually goes off. I though my phone finally broke as I tried uninstalling and reinstalling apps, changing settings here and there to no luck. I finally realized about the beta Screebl I had installed, and decided to disable it. The moment I did that, the phone was back to normal, no weird things happening to it.
So try doing a factory reset first before sending it back.