USB-Stick not recognized, can not dd

Hi, i inserted a USB-Stick into the PC, now it is not recognized.
If i try to do a

1.cfdisk, it gives an error:
"Error: Error opening /dev/sdc: No medium found
Invalid device"

2. dd:
dd: opening `/dev/sdc': No medium found

3. fdisk :
Error: Error opening /dev/sdc: No medium found
r Retry
c Cancel

but the device is showing in /dev/ - directory..., an
.

I was able to access it earlier, but now i got stuck.
Any instructions , or help ?