Time for some basic network diagnostics:
Start with the computer unplugged, go to Network and Sharing Center and get to the adapter properties for your ethernet/wifi adapter. On status, note the IP address (IPv4). Windows has one it uses when it hasn’t been given one, just keep that in mind for now. Mine comes up as 169.254.94.92 when disconnected.
Connect wifi / cable and give it a minute for the router to assign an IP address.
Check the IP again. Typical internal IPs are 192.168.X.X series, or 10.0.X.X series.
Have one of those? Router function is OK, on to the modem.
Still have that windows default IP? Router side isn’t doing it’s job, I’d look up how to factory reset it.
Okay, so let’s assume the router side works - you have an IP address.
Let’s try to log in to the router. If you have a 192.168 series IP - check the third digit group. Is it a one or a zero? Note that. Now, change the fourth group to 1.
IE: 192.168.1.1 or 192.168.0.1
Throw that in the browser ex: http:// 192.168.1.1 (omit the space)
All going well - this is the router login screen. You may have a password, maybe it’s taped on the bottom, maybe you need to look up the password like this: Provider Modem Model Password in google.
If you can log in, look for a WAN or “Public” IP address. This is you address to the outside word. If you got one - it’s at least connecting. You can try to factory reset it, just in case. If not, you have bigger problems - time for tech support.
If you do log in to the modem, sometimes you can dig around and find signal levels. Mention those when talking with the techs, they may be able to use that to find which section of cable is bad by checking signal levels at each junction between you and them. Had that done before!