Hi,
I use my onboard LAN connection to connect to my adsl router, and it constantly pops up with a tooltip from the LAN connection icon in the taskbar saying that the cable has been disconncted. This only lasts at most about a second, then it shows the tooltip saying LAN connected. This only happens with one of my computers, but not the other one. Its not the cable as I've tried swapping them. I've also already tried updating the onboard LAN driver. Does anyone know what I can do? Thanks in advance.

If you have checked your hardware (cable and onboard LAN) then I would simplely throw a new Network (LAN) card in your box.
These are relatively cheap and extremely easy to install.

In other words, your ADSL "modem" is connected to the Ethernet port on your motherboard? Sounds like a bad cable or port.

One other possibility is that your onboard LAN is configured for 100Mbps Full Duplex while your ADSL is configured for Auto-Negotiation. What will happen in this case is that the ADSL will negotiate to 100Mbps HALF duplex. The connection will still work but if you put any kind of load on the connection you might get the behavior you're seeing. If this is the case then set your Onboard LAN for AUTO to match the ADSL.

Casey

Oddly enough, I checked what cajalat said, and it was already set to auto, so I did the inverse, and set it to 100mbps, and although it didn't seem to fix it completely, it did seem to make the message appear less.
I would like to try and fix this without buying a new NIC, however I might try a friends one to see if it does the same thing to determine whether the onboard ethernet port is faulty, and then report back here.

NIC's are $15...

Is the message worth that? Doesn't work, return it. We call it an RMA...

Well I put another NIC into the computer, and the message doesn't pop up anymore, so must just be a faulty NIC. I thought it might have been software related, so that's why I sought a solution through mighty Google, and forums...