*Most routers advice to NOT turn off the router during the firmware upgrade. Most chances are that you bricked the router.* Disconnect everything. Unplug the router. Wait for 30 seconds and plug it back in. Wait another 30 seconds for the router to boot up. Press and hold the reset button for 30 seconds. Connect your computer directly to one of the router's LAN ports (not Wi-Fi) with an Ethernet cable. Open a browser and type in the address field 192.168.1.1 to access the the router. If you don't get the password field the router is bricked.

  @Gen-z 

 

Unfortunately lesm is right, this could have resulted in a corrupted firmware

 

The best option for you would be to try the factory reset via the button on back, that might restore the old firmware.    Failing that I would contact / email support and see if they can help you in any way.