Since you said you can connect from wireless client, do the following from a wireless client:
1) pull up command prompt: Start > Run > type in 'cmd'
2) at prompt, type in 'ipconfig /all'. Take a note of the Default Gateway field, something like 192.168.x.1
3) open up browser and type in like 'http://<your noted gateway IP>'
4) when asked for passwords, type in default password. If you don't know, google 'default pass zyxel <your router> series'
5) when you get into admin pages, check that LAN ports are not disabled. If they are enable them.
Even after you enable them and still can't access through LAN ports, then most likely that your router is faulty.