Tearing my hair out

Please, please see if you can help me!

My desktop PC has a rather flakey wireless connection, as the router is at
the other end of the house. Eventually, I ran a network cable from the
router to the PC. Unfortunately, Windows still seems to prefer the wireless
connection to the cable.

Specifically, if I disable the wireless connection, I can connect to the
router using the cable connection, but I can't get beyond the router to the
outside www. I can ping the router and get a <1 ms response, and I can bring
up the router's admin screen.

I thought that maybe this is an issue with the cable or the router, but if I
plug the cable into my laptop it connects just fine.

Any ideas please?

GB