SR-71 Blackbird said:
Try disabling Task Offload. Go to Device Manager, and properties, than Advanced, and turn Task Offload off.
Try this ^
This is a good recommendation.
Regarding the earlier question about why other stuff works properly, power issues can have some very odd negative impacts that can be very difficult to resolve. Without a solid power foundation to work from, it can be next to impossible to figure out what is going on.
That being said, if the on-board network adapter has become defective, you are going to have to change to alternate means to connect to the net. I would suggest you check with a friend where you live to see if anyone has an adapter you can borrow for troubleshooting is area51reopen's suggestion doesn't solve the problem.