A few days ago I dropped my 5D3 from about 6 inches.
When I turned it on, the read/access light (you know the red one) wouldn't stop flashing. Well, it wouldn't stop flashing when the CF card slot was selected.
I tried turning the camera off and back on again. Nothing.
Same for taking the CF card out and putting it back in.
Same still for choosing the SD slot, doing on-off, and then choosing the CF slot again.
So, in the end I backed up my photos and reformatted the CF card.
THAT stopped the flashing. And it hasn't flashed again since, except for the times it does in normal usage.
But my question is — anyone have any idea why the light would have been flashing constantly? It didn't change anything w.r.t. functionality, i.e. the camera still took photos and could write to the card. The light simply kept flashing.
I tried researching the problem online and came up empty. The manual is equally useless.