Bricked DSGW-090-2 after firmware upgrade

I tried to follow that guide. I don’t have USB-to-serial bridge connector.
I tried to access the Gateway wth ethernet cable and set my IP to 192.168.0.222. When I try to access 192.168.0.250 I get no response. The power led signal on the gateway is allways turned off. Only the network led is on, after power connection.