First time posting on this forum so bear with me...
I am having the same type of problem with an onboard Realtek 8111C LAN controller on a Gigybyte motherboard, running Win7 64.
I did a clean install of Win7 on my machine and my network connections worked perfectly. The problem comes up each time I start up the computer up from being shut down. It doesn't happen if I do a restart.
Once the computer is booted to windows, I get no internet (or email for that matter). I am not getting any messages about adding new hardware. The hardware is in Device Manager, it just doesn't work. To fix it, I have to go into Device Manager, disable the device, then enable it and the controller works fine. Or - I can reinstall the drivers and it will work too but the next shut down starts the issue all over again.
I have downloaded and installed the latest drivers directly from the Realtek site but it didn't fix the problem.
Sorry I don't have an answer for you but know that you are not alone. Hopefully someone will be able to help...