Need help with connecting phone line to CGD24G – Wireless Cable Modem Gateway

Hi have a  CGD24G – Wireless Cable Modem Gateway provided by my cable compnay that is functioning perfectly and i have had it for about a year.  I recently was given the idea to connect it to my main PC with a telephone cord in order to connect the main PC to the internet and everytime i attempt to do so it will not connect and gives me "Connection failed with error 651".  Could anyone help me with this? This is still a Windows 7 PC if that helps in anyway and the phone cord I bought was a normal phone cord from Walmart.  Do I need a special phone cord in order to properly connect it?