This is mostly a customer to customer forum -- we are not Comcast.
Please read "Troubleshooting Suggestions for Connection-Related Issues" and "Information Required for Connection-related Posts" found at the top of the "Connectivity and Modem Help" forum page and follow the instructions.
1) Please connect your computer directly to the modem via Ethernet ( no router, no wireless, no USB ) 2) Run ShaperProbe and post your results. (It works with Win 7) 3) Post your upstream and downstream signal levels (click the link.) We are interested in your power levels (dBmV) and your Signal to Noise Ratio (SNR). 4) Let us know to what speed tier you subscribe. 5) Post the make a model of your modem. 6) Post your modem's error logs.