but I wonder which ports you are using in the 5 port switch. Often the last port is for uplink use and is shared with port 4 so only one can be active at a time. Make sure you are only using ports 1 thru 4. Another thing to try if you've not already done so is plug one of your other devices into the port your PC is currently using. Another place to look for clues would be in your router's web interface to see what devices show as being attached. This could take some sleuthing on your part.
In a room across the house I have a WRT1900AC Router plugged into a Arris comcast modem. I have a CAT6 cable plugged into the WRT router going around the house and into an extension of the house. The extension is separated by a brick wall so WIFI signal there is weak. The Cat6 going around the house is terminated in a TP-Link 5-Port Gigabit Ethernet Switch. To sum it up Modem<->Router<->Switch.
The issue is I have 3 devices connected to the switch; a PC, a Tivo, a Sony TV. The PC connects to the internet just fine, the Tivo and the TV both report no router. How can I make this work?