Why cant i connect to the internet, please help?

I recently got internet from sudden link, they provided me with a modem, I just can't get onto the internet for some reason. The power, receive, send and online lights are fully lit except for the pc/activity which keeps blinking when I plug it into my computer or xbox. I called sudden link to register my modem and gave them my HFC MAC ID #, the tech told me to wait 15 minutes and try again, it didn't work. I have a split coaxial connection also connecting to my TV for cable. When I install the software to my computer, the system tells me there is little to no connection and doesn't connect.