Yep same problem here, had to pull battery once.
Now because I'm new here don't bash me too hard when I say that,(because this may be very well known) first, I have noticed that when i put it in sleep mode it takes a very long press on the power button to get it back to life.
I have also on two occasions noticed it did not turn on right away and I held down the power button for about 15-20 seconds and it turned on no problem, this was not from a sleep state.
Now because I'm new here don't bash me too hard when I say that,(because this may be very well known) first, I have noticed that when i put it in sleep mode it takes a very long press on the power button to get it back to life.
I have also on two occasions noticed it did not turn on right away and I held down the power button for about 15-20 seconds and it turned on no problem, this was not from a sleep state.