ATT Note 3 Lollipop won't turn on

All of a sudden, phone just died (battery was over 50% at the time). no sign of life, can't go in to boot mode, recovery mode or any other mode, doesn't show that is being charged (2 oem chargers tried, both working fine with S5 ). plugged in to laptop usb port - shows usb device is not recognized. any solutions? thanks