1. Are you their IT? User? Friend?
2. Do you have Cox Home or Cox Business?
3. If the later, do you have a static IP or DHCP?
4. If the later, are you connected direct through a switch? Or something managed?
So far all evidence stated points to a configuration issue with the *new* client on the *new* OS, perhaps because, as you stated, the IT is not familiar with the ISP? I assume they are more used to DSL? With Cable its alot easier. You can pretty much rule out the modem and the ISP. JMHO. I would maybe look to Windows Firewall? That got a huge change between XP and Windows 7. Also does the client do any error reporting and logging? If so