The vast majority of ISP’s only support 1 public IP address. So unless you pay for more (most don’t allow it) or have a business account, only 1 device can be connected to the modem and get that public ip address. So what you’re experiencing is normal. connect the desktop to the router. 

FYI Others in this forum have also had issues when trying to connect to the secondary ethernet port on the S33. My understanding of the issue is that in order to use both of the ethernet ports on your S33 to connect to the internet, your internet provider needs to provision two dedicated IP addresses, one for each of the two S33 ports.

You could try the following; Connect your wireless router to the primary (yellow) S33 port. Connect any additional hardwired devices to another port on your router, maybe using a switch if necessary.

Hope this helps. Good luck.

Not all ISP’s will provision with 2x public ip addresses. And if they do, many times they charge you for it. Something to keep in mind. 

It is always best to go modem--->router---->devices just for the firewall the router brings to the equation. leaving a pc direct connected to the modem removes the firewall and can leave you open to exploitation. (especially if you don’t know what you’re doing)