could the card have lost its partition table? if possible, put it into a USB card reader, insert into a linux box, do "fdisk -l" and see if it reports a drive with no or a corrupted partition. then use "fdisk /dev/sdX" and delete/recreate the partition, then format the new partition with "mfs.vfat /dev/sdX1".

YMMV. actions taken at own risk. blah blah.