This also happens when you leave it undocked for months and let the battery die totally lol. For some reason when it is really flat it doesn't detect that it is being charged.
You have to hold the power button down for like 30 seconds then plug it straight into the charger for about 30mins to an hour and hope it works lol.
At least with mobiles they detect that there is charge and you know it will take a while before you can boot it up from a long state of being flat for months.
Mine actually has something akin to that problem whenever I allow it to run out of battery power while in standby mode and then attempt to start it when it's plugged in, but I've since found that if I just plug it in and leave it on the charger for a few minutes it's able to boot up properly. This is a problem that has persisted through multiple patches and definitely scared me the first time lol