Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I think that your main PC has been connected - by WiFi I presume? - to the wrong router by mistake.
You need to, first, disconnect it from that router.
Then, you need to go into your Connections (or Network Connections) and remove the WiFi connection to that router.... but this process could be the wrong thing to do if you do it wrong, so please tell me your Windows version, on your main PC, and I will instruct you as to exactly what to do.
(In outline: you don't need to remove your entire WiFi connection. Rather, you need to disable the connection to the wrong router. It's a simple process, but varies a lot in detail between Windows versions.)
After that, connecting to the right router (provided it 'shows up') will fix matters.