My phone will not power on. It has no problem charging or operating when on, but as soon as it is powered off, it cannot power on again. The red light is on, and I hold the power button for 15 seconds and it shows the white zte screen for some time but instead of showing the at&t screen, it goes black and the red light is on. I can not power on my phone. Please help because I am not looking forward to buying a new phone.