Hello everyone, I have been experiencing the exact same problem. Unless I missed where someone mentioned this, it is more than just the network adapter. When this problem randomly occurs the USB 2.0 ports are also disabled during boot. I know this because I cannot access the BIOS with my USB keyboard when it happens. The weird part is the USB ports are enabled when Windows starts, the network adapter is not. My solution is the same, cut the power and it is fixed, just rebooting will not fix it. This has been happening to me about once every 10 boots or so, but there is no pattern or cause that I can observe.
This is a very big problem for someone wanting to rely on a machine remotely. I am able to wake on lan and the computer starts, but when the problem occurs it starts with the network adapter turned off and thus I cannot use it remotely.
Thanks for any suggestions or ideas...