Why does my Iconia A500 occasionally stop responding?

I have an stock-standard Acer Iconia A500 32G WiFi-only tablet. The screen usually turns on immediately when I press the power button. However, it sometimes refuses to respond and I have to hold done the power button for a few seconds, then release it and hold it down for a few seconds again. At that point, there'll be a vibration and the tablet will boot through the Acer and android screens. My thoughts are that the first sustained button actually powers it down forcefully and the second brings it back up (but I can't be certain of this). Does anyone know why this would happen? Are there any things I can look at on the file system to see what's going wrong. --- To elaborate on the non-responsiveness issue, while in most circumstances a quick push of the power button will bring up the PIN entry screen, it doesn't do so in the problematic cases. In those cases, the screen just remains black no matter how many times I push the power button. That's why I then have to do the long-press twice to (presumably) force shutdown and restart.