BINGO!! This was my first thought.

Do an ipconfig /all on your computers and compare the data from them.

Are they all in the same subnet? (i.e 192.168.x.x - One may be 192.168.y.x)

Make...

It sounds as if you have just the one computer AND your cable modem. If you want to share your internet connection (wired or wirelessly) you will need something to route your traffic for you....

168.254.2.237 - Geo Information
IP Address 168.254.2.237
Host 168.254.2.237
Location US, United States
City Tampa, FL 33601
Organization Hillsborough County Public Schools
ISP...

That was going to be my next suggestion - check the FW settings ESPECIALLY on Norton Internet Security. I have seen this app block things that are normally not supposed to be blocked. Im sure you...

Please dont hijack threads man... This has nothing to do with the post at hand, and you are basically asking us to do your work for you.
Google is your friend...
-Me

You may want to check a couple of things on the router itself -

MAC Address Filtering - Ensure this is not enabled. (Doubt it is if you can connect with another computer)

Remove the settings...

If you have 2 computers (only one connected to the internet) Then using a switch will only allow the 2 computers to talk to each other. (Given they have a trust relationship)

If you are looking...

My full time day job is in the world of IT, and with this of course comes all of the antiquated hardware still 'waiting for a purposeful *nix box' or something of that nature. At any rate, on with...