I have a Canon 80. Bought last August, still in warranty. Never dropped it, was never exposed to high humidity / cold / heat / dust. I always treated it with great care.
Yesterday I used it for quite a while to take videos. Each single video was less than 10 mins on average. Maybe a bit over an hour of overall video taking but the camera was turned on for a longer time. I also shot 3 photos (but in liveview mode). Everything worked as usual. Room temperature was around 24 degrees, nothing extreme.
This morning when I tried to take a picture through the viewfinder the camera locked apparently. After pressing the shutter the image was not previewed and then none of the controls would work anymore. I turned it off and heard the mirror unlocking. Turned it on again and shot some photos in live view, all fine.
I checked in the menu and turned off mirror lockup (I had turned it on in a previous session). With mirror lockup off shooting with the viewfinder works fine.
Turning mirror lockup on caused the same problem again: shooting through the viewfinder locks the camera. When activating the shutter you can hear a small mechanical sound but not the complete sound that I usually hear. After restarting the camera I checked if the picture had been taken. It had not.
Previously I have used mirror lockup in a few occasions and it always worked fine.
What I would like to ask is: should I check other settings that would explain this behavior or should I just contact Canon maintenance service to have it fixed?