Okay, let's get a teensey-weensey bit more specific. If you have blinking lights by the port, I'm guessing you're connecting through the ethernet port, correct?

First thing to do is call the support line for your cable company and go through the script with one of their Hindustani helpers. Since your setup is so simple (one modem, one computer, no router) it's likely they will be able to fix it immediately.

If that doesn't work, at least you will have eliminated the cable modem/cable company/basic network settings as a culprit.

So call the support line, do what they say, and please report back to us if we can help further.