I'm hoping it's not a blown Ethernet port on the iMac; however, if it is, it's better to know that.
Some things to check:
If you can find the hardware diagnostic CD that may have come with the iMac, try booting from that and running a full set of tests.
If the router has link lights for the Ethernet ports, make sure yours is on. Try swapping ports on the router, try swapping cables.
You're running Mac OS X, I'll guess. Open the "Network Utility" (It's in Applications:Utilities) and see what it says about the "en0" network interface.
no subject
Some things to check:
If you can find the hardware diagnostic CD that may have come with the iMac, try booting from that and running a full set of tests.
If the router has link lights for the Ethernet ports, make sure yours is on. Try swapping ports on the router, try swapping cables.
You're running Mac OS X, I'll guess. Open the "Network Utility" (It's in Applications:Utilities) and see what it says about the "en0" network interface.