Galaxy S6 :: Why Won't Screen Turn On After Being Left Idle For A Few Hours

For the past month, my galaxy S6 has been having problems. The screen won't turn on when I press the home or power button. Also when I plug it to its charger, the screen still won't turn on and the LED won't turn red as well. When this happens, I know for a fact that the phone is still turned on because the notification light blinks because of the received notification sometime during its idle time. Here's what I've tried so far:

- I am able to force reset the device by holding the power and volume down button until it restarts. I felt relieved that I am able to restart my phone when it happened the first time but pretty annoyed when it kept on happening.

- I tried clearing cache partition in recovery mode. At first I thought it worked but still...

-I already did a factory reset (twice) but right after the latest hard reset just 3 or 4 hours into it, still screen won't turn on.

- Earlier I thought that it was because of the notifications I was receiving while I was asleep (viber, facebook, sms) since when I woke up in the morning and the screen won't turn on, I had pending notifications. But recently, the screen won't turn on after being idle for a few hours without received notifications.

At first I thought it was a software issue but I'm starting to think that it might be a hardware issue. I'm planning to take it to Samsung in a few days if the problem won't go away. My device is not rooted by the way.