This issue has been reported before; take a look at the following thread: Edison unable to make it as external drive
I recommend you to try to re-flash your Edison. There are different ways you could try to re-flash the module:
- Using the Flash Tool Lite. This is the usual method to flash the module. You can download the Flash Tool Lite from the following site: IoT - Intel® Edison Board Download | Intel® Developer Zone
- Using the flashall script. This is an alternative method that you could try if the Flash Tool Lite doesn't work. Check the following document where there is a description of this method: How to Run the Flashall Script
There are a couple of additional suggestions in the thread I mentioned above. I recommend you to check them.
Also, if you have access to different Operative Systems I recommend you to try the flashing methods in each OS. Some users have reported that the flashing methods didn't work in a particular OS, but when they tried them using another OS one or both methods worked.
Make sure the USB cables work properly and the module is powered up correctly. If you are powering the board only through the USB port, I recommend you to use a DC power supply instead.