Hi SpyJoe, and

to CF.
I'd suggest you try disabling and uninstalling any firewalls you've got - they may be blocking the DHCP messages coming from your ISP. If your friends laptop works on the cable modem, you're right that it can't be the modem or Ethernet cable at fault, however there is a possibility that it's the Ethernet card in your computer. Is it possible to connect your cable modem via USB? If so, try this, just to rule your NIC out of the equation.