I had a most unusual problem after updating my laptop to Windows 7. The purpose of a laptop is really to move around so I usually take it from my workplace and use it at home, carrying it back on the next day.
I found out that, whenever I booted up the machine before plugging the network cable in, my network adapter vanished from the notification area as well as the Network and Sharing Center. A reboot, with the cable already plugged in, solved this little annoyance.
But, sometimes, the problem has it source between the computer and the chair. I was not aware of a nice feature on Power Management that allows the computer to turn off a device to save power.
So I just had to take the check off the turning off option and the situation ceased to occur. Maybe someday I’ll put it back on 😉