1.7 The RESET Button
If you forget your password or cannot access the Web Configurator, you will need to use the RESET
button at the back of the device to reload the factory-default configuration file. This means that you
will lose all configurations that you had previously and the password will be reset to “1234”.
1 Make sure the POWER LED is on (not blinking).
2 To set the device back to the factory default settings, press the RESET button for ten seconds or
until the POWER LED begins to blink and then release it. When the POWER LED begins to blink,
the defaults have been restored and the device restarts.
The default IPv4 address is 192.168.1.1
As that is otherwise used on my LAN, one of the very first tasks I performed was to change the address to 192.168.1.254
I wonder . . . are you seeing the GUI? Perhaps you could do an nmap scan for the entire 256 addresses of the 192.168.1.X sub-net. For example, this is what I see --
[Duo2 ~]$ nmap 192.168.1.0/24
Starting Nmap 5.51 ( http://nmap.org ) at 2016-10-01 16:13 BST
Nmap scan report for Duo2 (192.168.1.3)
Host is up (0.00051s latency).
All 1000 scanned ports on Duo2 (192.168.1.3) are closed
Nmap scan report for AP (192.168.1.254)
Host is up (0.028s latency).
Not shown: 994 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
23/tcp open telnet
53/tcp open domain
80/tcp open http
443/tcp open https
Nmap done: 256 IP addresses (2 hosts up) scanned in 4.34 seconds
[Duo2 ~]$
There are only two devices currently active on my LAN. This laptop (with the 192.168.1.3 IPv4 address) and the ZyXEL VMG1312-B10D (with the 192.168.1.254 IPv4 address). I have deliberately enabled all management ports (bar SNMP) on the LAN, so the above port list shows what should be available to you.