Switching to Cable

I'm having a problem and I'm not sure if it's my PC or the actual modem (I'm checking here first because the modem techs usually know nothing).

When I first purchased my Dell PC, I already owned a Compaq PC that was already connected to the internet through local cable company's cable modem! So I used dial-up on my new Dell Pc, but before I got dial-up I would switch the cat5 cable between the two pc's. Now that the Compaq is practically trash I want to use the cable modem solely for the Dell...but the modem PC light doesn't light up when connected to the Dell..I'm wondering if this is a modem issue (I doubt), or something I need to change on the PC...the modem worked fine on a friends laptop but will not connect with my Dell. Please tell me if there's something I can do aside from spending hours talking to my ditzy cable company reps!!!

Thanx in advance!