I first encountered this problem on an XP PC where all of sudden the NIC lost all functionality but on the surface, it appears to be functioning properly as it continues to show link (light) status and even if you do an ipconfig /all it will show an IP address if your connected to a cable modem or LAN connection. The problem, however, is when you launch the browser - it comes up with a DNS error, can't connect, ect.. and if you try to release or renew the IP address it states something to the effect that the card is not in a permissable state and has failed to obtain a new IP address. This has happened to me three times so far. Troubleshooting has included, new NICs, relocating to other PCI ports, re-installing TCP/IP settings, disable - re-enble the NIC and finally, last resort, fdisk-format-reinstall of the OS....doo da doo da! I'm not sure what else to try and any help would be most appreciated.
Go to the Run dialog box (Windows Key + R) and run a command prompt box (CMD).
Type (allowing each command to complete before continuing to the next):
I hope that helps that problem out. If it does persist though, give your ISP a call. And make sure that if they tell you to try "ipconfig /release" and "ipconfig /renew", that you've already tried it to no avail.