I have a Rebel t4i. when I turn it on it says card not formatted and will not format for me.

[Phili]

Rebel t4i will not read sd card and also will not format for me. Have tried both new cards and old cards. Not sure what to try next.

[Skirball]

Are the slide locks on the SD card set to 'Lock'?  It won't format when protected.

Also, I've had cards that the switch broke on and was finicky.  Sometimes I would have to have the switch somewhere in the middle in order to work properly.