I am having the same problem with my 70D. I was changing my picture profile when the camera locked up on me. I have tried all of the things listed above (or below), but nothing seems to work yet.
I have also tried to reset the whole camera, by clicking the option: remove all camera settings.
This also did not work. I don't get why but sometimes the thing won't even turn on with a fully charged battery, with or without lens attached.
I've swapped SD cards, erased them, formatted them, but nothing seems to work so far.
When I am in movie mode or in LV mode the camera freezes after a couple of minutes or sometimes seconds. Then the screen freezes, but I am still able to change settings from the top screen, so thats weird..... and then the error 80 appears. When I turn off the camera the screen stays on and frozen and remains that way until I remove the battery.
I've had this problem since three days from posting this, Please help. :(
Thanks in advance