Is it wifi or wired? Wifi is easy to diagnose/troubleshoot but wired setups can be far more difficult (more points of failure & harder to track down easily). I could be free for a couple of hours next week to assist, just pick up a beer for me and we can call it even. :)
In the short term, have you tried a hard reset on your modem & router? Depending on the model of router, it should have a serial sticker on the back or bottom which should also have an address (http://192.168.0.1 is most common) and you should be able to login through the router’s own page then check the settings, connection quality, etc. Could help you narrow down what the problem is.
Let me know if you still need help next week!