It sounds as though your computer’s network card is working normally and you said you’ve swapped out the ethernet cable. Assuming you’ve tried powering down your modem for two minutes and had no luck, I would start suspecting that it has a hardware failure, as it doesn’t sound like there are any software issues with your PC. Do you have another computer you could try to connect to that modem to see if it will connect? Alternatively, is there any other location (at a neighbor’s house, your office, etc.) where you could try connecting your computer to a network to see if it works there? If not, you may be stuck with having to reach your provider’s tech support.
I would be strongly suspecting the modem at this point. If you rent, your service provider should swap it out for you. If you own it, you may be on the hook to get another one; hopefully you have a local store with a decent return policy so you can bring a new one back if it doesn’t work either.
Based on troubleshooting, I think I’m going to have to try a new modem. There is only one place allocated for a light on the modem, but it’s for power, not for connectivity.
Based on everything I’ve done, it likely is not the network card (since it claims to be enabled and working fine).
Thanks everyone for your replies. Very much appreciated. If I find out the exact cause and problem and can fix it, I’ll post back with the details.