I hooked the iMac to the router and I don't get a light. To be sure everything was good with the cable and that port, I hooked the MacBook to it, this time I got a light. Must be something with the iMac then.

No matter, I was planning to upgrade to AirPort anyway. I don't want to upgrade if the motherboard is failing, and the ethernet was just the first to go.

So, what could have caused the ethernet to fail? A failing motherboard? A spike through the port?