How will i unlock a memory card in SD 790 IS canon

All SD (and SDHC) cards have a locking switch on them and this can be activated accidentally when handling the SD card.

Remove the SD card and slide the switch on it away from the lock position. If this does not work or if the switch is already in the correct position, then slide it all the way to lock and then fully back again.

If this fails then you have a faulty SD card and must replace it. Dirty electrical contacts do not result in a card locked message so you won't have to worry about those but as with all memory cards never touch the contacts unless they clearly need cleaning. Note that if you have to replace the memory card you can use regular SD cards up to 4GB and SDHC cards which start at 4Gb rising to 16GB maximum. The camera slows down when using SDHC above 8GB though.

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