Bought a "Excelvan 7" 4.0 android tablet" worked fine for a few days and then started doing this. Basically it starts to turn on flashes up the excelvan screen, then the android screen. the moment it finishes loading the android screen, it turns black and seems to be turned off. The instruction manual is very badly wrote. I cant find how to "hard boot" it and have tried practically every combination of the vol buttons and power button combined. Would be very grateful for any contributions on how to fix this matter.