I got an error today where my Edison was not showing on the explorer.
First thing to do is to se if the FTDI connection to the Edison is working.
Then power the board up, all start up data is then shown on the FTDI connection, look for any error.
My error was "[FAILED] Failed to start Load Kernel Modules."
The only way to get this working is to use Intel Phone Flash Tool.
First download an new image for the Edison
Link: https://software.intel.com/iot/hardware/edison/downloads IoT - Intel® Edison Board Download | Intel® Developer Zone
Extract the .zip file to a location you find it and use Flash Tool to flash the Edison (.json file).