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I was having a similar problem with my 60D. I would put it in the card that had ML on it and nothing happened, wouldn't turn on. But if I took out the card and removed and put back in the battery it would turn on. But it would work with other SD cards, so I put the card into my computer (I have a mac) and opened up Disk Utility. From there I just erased all the data even though I deleted everything prior. That seemed to work. If you can find a way to format your card other than using the camera it might work. This also happened to me after I used the card to transfer some photos.