I have DSL and don't use any software. Does your documents say what the IP address is for your cable modem? Sometimes my DSL router hangs and I unplug it for a minute and plug it back in and all is well. This's from Comcast:
"I cannot establish a connection to the Internet. What should I do?
Leave your computer on and unplug the power to the modem (only the modem) for approximately one minute. Plug the modem back in and try to reconnect.
If the connection still fails, do the following: With the computer on and modem power on, press the reset button on the back of the modem (it is a small hole in which you will need to insert something equivalent to the end of a paper clip) for approximately one minute. When you let go you should see the top three lights lit up solid green. If the connection still fails, contact a technical representative at 1-888-Comcast for further assistance."
This is how I'd test to find where the connection is bad after resetting your cable modem and you still can't connect to the internet.
If that doesn't work try finding out the IP address of the cable modem. I have a couple of PCs, a wireless router, and a DSL modem configured to connect to the internet. If I run the command ipconfig in a command prompt window, it will tell me the IP adress of my PC and gateway ie "my wireless router". I can run the command ping 192.168.0.1, and if it replies I know the connection is good from the PC to the wireless router. I can then try to ping my DSL router to see if the connection is good through the PC, and wireless router to the DSL router. This is done by running ping 192.168.1.254, which is the address of the Westell DSL router. If I get replies here then I know the connection is good to the internet. The final step would be to see if you can ping
www.yahoo.com. If this gets a reply you are good to go since you have sent a packet of data from your PC, through intermediate devices, out to the internet and back to the PC. A failed reply in these steps would tell you where the problem is. Of course your system and addresses are likely different. If Comcast does not have documents showing the address for the cable modem, call them and ask. Also once you fnd the address of the cable modem, you might be able to access the address for a configuration and testing page, firware upgrades, etc. Comcast has to help you out to get connected.