Forti wlc 50D is not booting

If cable and switch are working are you able to reach the Forti wlc 50D by IP address?

The Forti wlc 50D should come with a serial (rollover) cable that you can use to connect to the console port, though you may need to get your hands on a serial-to-USB adapter.  Using a laptop (or computer) connect to the console port and run (say) Putty. Powercycle the Forti wlc 50D and watch the console output for any errors.