Unstable network

Hey

I recently begun having a problem with my network. I have two NIC's. One is the onboard intel one (82566DC), the other is a cheap one I bought a while back that I recently put in to see if the other NIC was the problem (Realtek RTL8139).

I keep getting a network cable unplugged balloon tip. Obviously both are connected to the router. It seems that it works well on 10mbps full duplex, but when I bump either of them to 100mbps full duplex, I get these error messages. I used to stream movies and tv shows to the computer I had connected to the TV over the network, but now the movie playback is very laggy, and I'm guessing that this is because of the reduced network speed.

Is there anyway I can fix this?

Thanks very much.