I just got my Zenithink C91 Upgrade. My wife and I were both really excited about it as it is our first tablet. Problem started showing up on Day 2. A green band appear at the bottom of the screen while starting up ("Android" screen). We later noted that it may be related to tilting the tablet while starting, so we avoided doing it. But now, the band seems to appear more often, and came in different colors (red, yellow...) And sometimes the whole screen turns to that color. Have anyone had the same problem before? Do you know what is the cause of that and how can we solve that? Thank you!!