If only you lived slightly closer to me i'd give you one. I got tons. used to work in cabling infrastructure and still in IT.
I was going to say try replacing the cable, but if it was the cable it seems like it would be on all servers, not just this one. but just to get everything out of the way it couldnt hurt.
also monoprice is the best place to buy cables.
Also to hit on Bill's point if you don't have docsis 3 modem, get one.
If you have time warner and go to the customer service center and tell them you want one they might upgrade you for free. They did for me no hassle, but wouldn't over the phone.