I have a Centon Flash Drive that will not mount. It is not readable on the iMac nor a Windows 7 machine. The drive cannot be reformatted by the Windows or IMac usual methods that this layman tried.
Can you get the disk identifier? In Disk Utility, select the drive and choose "Info" – it should read something like disk1 or disk2 or so. (But NOT disk0; that's your internal HD!)
Then open a terminal, and type in
sudo dd if=/dev/zero of=/dev/diskX
(where diskX is of course the disk identifier you got earlier.)
Type in your admin password, and it should overwrite every block of the disk with 0x00 (i.e. erase it).
Then, you can format your drive.
[Please be cautious when doing this; I'm not responsible for anything if anything goes wrong ;-)]
I have OS X 10.6.8.
Will you tell me if I should try this and if yes, how do I "open a terminal"?