Hello Diane,
As a test, you should turn off your computer, unplug the cable modem’s power. Disconnect the ethernet that is connecting the Eero to the cable modem and wire the cable modem directly to your computer.
Then power everything on, now you can test if your computer can get online. If it does not then you may have an issue with your computer’s networking that would need further troubleshooting.
If it does get online then power everything off again, wire the cable modem to your eero ethernet port 1. Wire your PC to the Eero on ethernet port 2, then power everything back on and you should be online.
Let us know how it goes, best of luck.