Networking DOA: Unidentified Network, Access: Local Only

Upgraded from RC2 to RTM a week or so ago. Networking was working fine for a
week and then after a reboot the network is no longer accessible.

Network adapter reports: "Unidentified Network" and "Access: Local Only".
Trying to renew DHCP fails and the adapter gets assigned a private IP (169).
Disabling/reenabling the adapter makes no difference as does uninstalling and
re-installing it.

Also saw some posts elsewhere suggesting checksum issue (someone else who
had the problem ran a network sniffer and observed all outbound packets had
zero checksum) or power mode issue (Windows powering off the adapter when
entering low power mode and not resuming it) so I tried disabling both TCP/IP
checksum offload and also removing permission for Windows to power off the
adpater when entering sleep mode; neither resolved the issue. Saw another
post saying that putting the PC into sleep mode and then resuming temporarily
(until next reboot) solved the issue but this does not work for me either.

Adpter is a Broadcom NetXtreme Gigabit Ethernet, driver is b57xp32.sys,
v9.52.0.0, 15 May 2006.