I have this same problem, just started a week or so ago. The only think that changed was I installed World of Warcraft Burning Crusade. Uninstalled or reinstalled in and that does nothing. My PC can only get a connection through the usb connection, not ethernet. I have tired a new ethernet cable and its the same results.
ethernet- ipconfig/all as follows
Microsoft(R) Windows DOS
(C)Copyright Microsoft Corp 1990-2001.
C:\DOCUME~1\ME>ipconfig/all
Windows IP Configuration
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usb-ipconfig/all as follows
Microsoft(R) Windows DOS
(C)Copyright Microsoft Corp 1990-2001.
C:\DOCUME~1\ME>ipconfig/all
Windows IP Configuration
Host Name . . . . . . . . . . . . : hithere
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : cfl.rr.com
Ethernet adapter Local Area Connection 3:
Connection-specific DNS Suffix . : cfl.rr.com
Description . . . . . . . . . . . : Scientific-Atlanta WebSTAR 2000 seri
es Cable Modem
Physical Address. . . . . . . . . : 00-1C-EA-3F-25-83
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 67.8.231.150
Subnet Mask . . . . . . . . . . . : 255.255.248.0
Default Gateway . . . . . . . . . : 67.8.224.1
DHCP Server . . . . . . . . . . . : 10.118.64.1
DNS Servers . . . . . . . . . . . : 65.32.5.111
65.32.5.112
Lease Obtained. . . . . . . . . . : Wednesday, July 23, 2008 3:26:03 AM
Lease Expires . . . . . . . . . . : Wednesday, July 23, 2008 3
27 PM
C:\DOCUME~1\ME>