If you tried reset but no luck, I think it is faulty totally.

I tried to reset while it is already powered, but there is no reaction.

When I press reset while at the same time powering the router on, the led corresponding to the port on which a cable is connected is blinking. It seems packets are broadcasted, but I don't know if it allows to reflash the device in this mode and how (maybe a remote console on the bootloader to download an image, or a tftp server listening, maybe waiting for a multicasted image,...).