Ethernet connection isn't working but regular wireless wifi is

My ethernet connection randomly stopped working. I've tried 2 different cords in all of the ethernet ports and it's still not working, I've reset the modem router combo completely and I've unplugged it and plugged it back in, still nothing. I have a custom modem router combo. I tried calling for help and the customer service representative didn't know about desktop computers or how they need a wired connection without an adapter so that wasn't helpful. Any help is appreciated, thank you!