I should correct myself. I was so upset about my camera not working that I posted before double checking the details. The first time, the SD card wouldn't lock into the slot, whereas this time it does but the camera won't recognize any of the cards...
I had this same problem a while ago. It was still under warranty and I sent it in, but they made me pay for it anyway. Now it has happened again. I have hardly used the camera in between these two failures - obviously there's some problem with it....