This is my issue: sounds similar...
I've just completed a build of a home PC with the P7P55D LE motherboard.
Previously I had XP on another PC and my internet was rock solid.
Now when I reboot my new windows 7 PC it reports that the internet is down.
I have to reset the router or sometimes by disabling and re-enabling the on-board NIC on the m/b it comes back up.
I have tried the following:
reducing the lan speed to 100 full.
disabling all the wol features
disablign the green feature within the network card.
Any ideas before I purchase a PCI network card to see if the problem IS the m/b?
Just to add when the internet locks up I can still access the Routers setup page via a browser session.
All the lights on the router appear as normal, however windows 7 reports there being a problem with the internet...which the "helper" tries to diagnose and comes back with "unknown error"