Typical failure modes, listed in no particular order, are Bad spot on the card (this can be handled with ZAR, esp. if not too many bad spots. Download ZAR now). Bad spot causing the card to lock up. I.e. once you accessed that bad spot, all read attempts fail till a power cycle. Device firmware problem causing the device to report zero capacity. This essentially renders the device inaccessible to any software. Mechanical failure – broken or jammed connection (most common being USB connector bent or broken loose from the USB stick).