The phone cannot be awakened from stand by, no matter the charge status when last used
Trying to charge the phone has no effect
Holding the power button has no effect, even holding for several minutes
Holding the power button and volume for 2 minutes does not start the phone in diagnostic mode
Random shut downs and restarts
Usually the phone will not charge - the white light in the top left corner is not lit when connected for charging
Wait several hours and then try to charge from power adaptor (not USB cable connected to a computer). If the light does not
come on wait a bit longer. Eventually the phone will accept a charge
Wait another several hours and then try to turn the phone on; the phone will eventually boot and the charge status
will now be at a few percent. If it does not boot wait a bit longer before trying again
Charge the phone up to 100%
My guess was that some system or application software gets stuck in a loop, consuming power until the phone
shuts down. So I started regularly closing unused apps and web pages to see if this had any effect, but
it did not.
My phone still reboots, turns itself off intermittently or sometimes turns off and won't turn back on.
At this stage, I think the only real solution is to get a new phone.