Camera Crash (5D3) What happened?

Yesterday photographing a wedding the bride and groom were beginning their walk down the aisle. My Canon 5d Mark 3 "froze-up". It kept saying busy in the viewfinder and the back screen was like noise from a 1970's TV screen with no reception. I turned it off but it stayed "on". I dropped the battery out and put it back it and this corrected the issue for the night. In your experience / opinion, what happened?

My first move would be to re-flash the firmware. Hope it goes away.

Canon made a 14mm fisheye? 15mm, perhaps?

WAF wrote in post #18478181
My Canon 5d Mark 3 "froze-up".

Were you using a grip, and if so what brand?

There is a fair history of people with similar issues that commonly involves use of a grip, often a 3rd party but some instances of the Canon grip.

No grip and no accessories except canon 580 EXII flash. Thanks for asking.

Done. Thanks for the suggestions.

I had this (not even switching off), BUT, I can't remember whether I had magic lantern installed or not. Probably, but in any case it sounds very similar to what can happen when ML goes 'wrong'. Since ML is just a additional firmware, then I would suspect that this was a firmware issue/bug/glitch. It may not be repeatable and may be a very specific sequence of things you did + settings.

Usually (well always for me over the last 6+ years) when this happens there are no lasting effects. I will always try to repeat what I did to help debug ML, but often I cannot and I never encounter the same problem.

Hope this helps alleviate a concern, and hopefully it was a one-off that won't reappear.