Did the process for update the firmware finished successfully?
Could you attached a screenshot of your Device Manager? It could be related with the driver and not the board itself.
You should use a 2.0 USB port, have you tried with different ports in your PC and with different cables?
You said that you can't boot from the SD card, are you able to interact with your board through the Terminal Console without an SD card? Are you following the steps from: Creating a bootable micro SD card for the Intel® Galileo board | Intel® Developer Zone