Unable to format pen drive

It sounds like you may have a broken pendrive; go to a terminal and try these commands; ensure the pendrive is in fact /dev/sdc 1st though (use mount):

sudo -i
fdisk /dev/sdc
p # Lists the partitions
d # This deletes the partition. Again, be careful you have the right one!
p # check...
n # Create a new partition
b # This one isn't a command, it's a type selection - vfat
w # Save changes

This should give you a list of partitions; delete the only one there (if more, repeat 'd' until there aren't - whilst being careful that this is definitely the right drive! It should then create a new one, set it to FAT32, and write it.

If that works, type fdisk -t vfat /dev/sdc1 ; exit & you're done.

If not, try cat /dev/zero >/dev/sdc & let it run for a while (-c when bored..) - if it generates no errors, try step 1 again. If you still get I/O errors, it's damaged.