If the camera gets too hot due to prolonged use of live-view or video shooting, you get an icon of a thermometer -- the icon is white. You should stop shooting and let the camera cool down.
If you keep shooting, you will eventually get a red thermometer icon and it may start blinking... if you ignore this the camera will shut down on its own (and then you have to let it cool down.)
If the camera freezes and the only way to unfreeze it is by ejecting the battery then it sounds like something crashed the firmware (ejecting and re-inserting the battery forces the camera to reboot -- the power switch is technically a software switch so if the camera has crashed, toggling the power switch will not be enough to reset it, but ejecting and re-inserting a battery will reset it.)
Whenever anyone has problems with cameras shutting down while shooting video I usually suspect a bad memory card.
Make sure you have a high quality card (don't skimp on cards -- especially if you want to shoot video. I use Sandisk Extreme Pro cards (yes, they are expesnsive.))
Perform a "low level" format in the camera. (don't format the card in the computer.)
Tim Campbell
5D III, 5D IV, 60Da
