Dead Phone for no reason

Recently my phone logged off by itself in the middle of the day. When I have tried to turn on the device NEVER came back on.

I have changed batteries, swapped SIM cards, and been certain that everything that I know of is in working order.

What can be the problem? Upon re-start I get a "Galaxy" screen, the NOTHING else appears. I have tried to go to my "reload/reboot" screen but all I can do is to remove the battery and restart with the "Galaxy" screen displaying for a few seconds ...then NOTHING else.