Receiving packets but not sending

I connect online through a cable modem (Time Warner Cable Roadrunner). The lights on the modem indicate everything is fine. I'm suppose to be connected once I turn on my computer but I'm not, and when I check network connections, it shows that I am receiving data but not sending. The only way to connect is to continuously plug and unplug the actual cable that connects my NIC card and my modem until it stats sending data. Eventually, I'll connect but I was hoping someone could explain this to me and figure out a way to fix it.

hmm.. are you "signed-in".. ? Also, to make sure, go to your modem settings page (usually http://192.168.0.1) and check to make sure your logged in