Suddenly, my 32gb Sandisk USB key stopped working on my Macbook. I plugged it in and it was not seen my the Macbook. It didn’t appear under the System Profiler, in Disk Utility nor in the terminal. After some struggling, I was able to make it work again.
Hot to fix the Usb drive not seen by Mac problem
It your Usb drive is not seen by your Macbook, open Terminal and run the following commands:
sudo rm -r /System/Library/Extensions/SATSMARTDriver.kext
sudo rm -r /System/Library/Extensions/SATSMARTLib.plugin
Reboot your Mac and the problem could be gone!