Sometimes the in wall wiring is done incorrectly or damaged. When I make a call on this there's always the issue of cost to diagnose. The more I have to do such as open up the panels to check wiring, the more it costs. Proper wiring is documented on the web so I'll stop here with the advice of go WiFi or just drop a cable.
My roommate and I are having an issue with our ethernet where a couple of times a day, our Ethernet will drop out and show the yellow triangle over the network icon. We have been in contact with our ISP for about 2 months now, and they're completely unable to fix the issue since it's difficult to duplicate. I am thinking it's an issue with the wiring behind the walls since no one else is really reporting this as an issue. What will happen is that the connection will stay up perfectly normally like it should be, and then at any point it could drop out. I've also tried just about every troubleshooting solution known to man, including manually setting the DNS, reauthenticating my computer, installing new network drivers, releasing and renewing the IP address, etc. Another reason I think this is an issue with the wiring is that last year, in a different building, I had no trouble with the ethernet. At this point we are completely out of options and don't even know where to start. A network diagnostic from windows says that the DNS is not responding. All I've heard from the ISP is to get a wireless adapter for Wi-Fi and see if that works any better, however I am partial to Ethernet as it is much more stable and reliable (in any other case). Is there anything we can do about this, or is it an internal issue?
One other thing: If I use a wifi adapter and ethernet at the same time, if one goes out, will it switch to the other without disconnecting?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic