I was having this problem whenever my battery died completely. Whenever I plugged it in it would automatically turn the phone on but there was not enough battery to get through the boot process and it would die again.. and because it was still plugged in, it would try to turn on again before it was ready.
Whenever this happened, my solution was to connect the phone to my laptop or computer for a few hours. It would charge much slower, but for whatever reason it would not automatically try to reboot.
I would wait for it to get to about 50%, then switch to the wall socket and let it do its "optimization" thing.