To which device is the TL-SG108E uplink port connected to? A modem? A router?

Dan Singer wrote

Its connected to a cable modem: Arris SB6190 and a Linksys WRT1900ACS Wreless Router. The router does not have internet access either.
Thanks!

Your ISP should have sent you instructions on how to setup a router / PC to be able to connect it to the cable modem. If it works when plugging in the PC into the modem directly, find its IP settings in your PC's network preferences and transfer this to the WRT1900 for the WAN network. You probably have to clone your PC's MAC address to the WRT1900's one if your ISP restricts access to your PC only. Then connect the PC to the LAN of the WRT1900, set up DHCP on your PC and try again. First of all you have to get Internet going and this depends on the technique and access credentials your ISP uses, so only your ISP can tell you.

Not sure wether it is a) one IP only or wether they b) restrict access to the MAC address. As for a) any other router should work also, since on the WAN interface every router just uses one IP (most often the one, which the cable provider assigns to it). Clients connecting on the LAN side get a totally different IP from a separate subnet with an own IP address pool, except if the router is configured to bridge the two networks together.

If it is b), on most routers there is an option to clone the PC's MAC address, but in your case you probably have to clone the MAC address of your ISP-provided router into WRT1900 to circumvent this access restriction. But I don't know the WRT 1900 in detail, so you have to find out wether it supports cloning of MAC addresses. Hope this helps!

I have confronted this type of issue one time before. To get rid of this, I have changed dynamic IP to static IP and everything is back to work normally.

Here are a few other solutions you might try:

https://usefulpcguide.com/18773/fix-ethernet-doesnt-have-a-valid-ip-configuration-error-in-windows/