to get you fixed (that worked for me):
- windows 7 doesn't come with any CDC (serial) driver
- download the latest adafruit driver package from here:
Windows Driver Installation | Adafruit Arduino IDE Setup | Adafruit Learning- install the package
- go in system manager and open the device list
- click on the Saber Core X peripheral (that is still with a question mark)
- select update driver manually => using a driver from your computer, from a known manufacturer
- select adafruit industries LLC and a board driver with M4 in it (like the feather M4 for instance)
- install driver and ignore the warning that it wasn't made "specially" for your peripheral
- eventually power cycle the board
- check system manager => devices => COM port : your COM should be there
tested with docklight to talk "ping" to the board, which answered "echo" as expected
(will add this in the manual)