Copy everything to your computer and make image of sd card just in case. Run program and issue command to restore partitions. You might be lucky to restore sd card to previous state
Use software called "test disk" for recover lost partitions on your sd card. For instruction how to use software find it on google. Its free and verry good. If your card is working chanses for restoring is high.
its a cable problem take other usb to mini usb cable and try . Make shure to connect to lower usb port on the Wii.
If you going to buy cable look for "Y" cable ."Y" cable is with 2 usb jacks second one is for extra power.