Why is my phone not restarting

after charging z5 alarm indicated completed. Phone was turned off and cannot restart.

Tried all Sony help descriptors ,10 sec power off, 120sec power off, connect to Sony Companion. Nothing helps. Phone is not picked up with the Companion software.

Looked at You Tube no help. Checked battery voltage after charging sitting at 4.09 Volts, This is well above critical min. voltage. Disconnected battery from motherboard, slight more voltage in battery.Reconnected battery, still unable to restart.

powered via USB connector no restart, NO power indicator.