http://www.nikonchat.com/nikon-coolpix-troubleshooting/
Nikon s4000 troubleshooting?
Ok so i was just taking a picture when my Nikon Coolpix s4000 gives me a
message on the screen that says “this card cannot be used”
I can’t take pictures access the menu, nothing at all
Only when i take the card out can i do anything.
I’ve tried flipping the orange little slip on the side back and forth
i can’t find a way to format the memory card
and i don’t want to buy a new card.
Is there anything i can do?
Please please help 
Sounds like your memory card went bad. It happens. You will need to replace the memory card.
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