On my home machine, I rarely reboot it. If a software update requires a reboot, then I do it. otherwise it stays running for weeks at a time. Vista (32-bit) has been stable enough for me, where I don't have to start the system or suffer system crashes.
But when I reboot, about 10% of the time (just a wildly inaccurate guess), the machine comes up without any network connectivity. In the past, I have associated it with Windows Update installing a wonky driver for the network card and I System Restore the machine back to normal. It happened today and the list of the usual suspects did not include any hardware updates. Time to dig deeper.
This machine has a NVidia nForce motherboard (Asus M2N-SLI Deluxe) and it has built-in dual Gigabit LAN controllers. I had an Ethernet cable hooked up to the first port and had disabled the 2nd one through Vista's "Network Connections" utility. My dead Windows Home Server box was next to my PC, so I unplugged it's Ethernet cable and plugged it into the second port on my machine. I enabled the network adapter and after a few seconds, it was live and had grabbed a IP address from router.
That was interesting. Since the working adapter used the same driver as the non-working one, that pretty much ruled out Windows Update nuking one of the drivers. I peeked at the driver settings for both adapter, they were both set to the defaults. I also checked the device status of the adapter, Windows reported that "This device is working properly." That was a pretty good indicator that the problem was not a fried controller on the motherboard.
The next thing to check was the ethernet cable. I swapped cables and there was no change. I decided to do the Nintendo fix. That's when you pull out the cartridge, blow on the connectors and ram it back in again. In this case, I disabled the adapter, waited 30 seconds, and re-enabled it. As Emeril says, Bam! The adapter started working. Time to start googleing and see if anyone else is having this problem.
And the number one hit for "nforce network adapter fails" in Google was a long thread in the Nvidia message forums. A sizeable number of people were having the same problem and they were all running Vista. It may be a timing issue during boot-up. Two workarounds were suggested. One was to change the duplex setting from "Full Autonegotiation" to "100 Mbps Full Duplex". The other was to change the priority order of the network adapter priority. I didn't want to mess with the driver settings, so I opted for changing the priority order. I'm not confident that it will fix the issue, but it wont hurt anything. Right now this is more of an annoyance than anything else, but I would like to resolve it permanently.