I recently moved my iMac from the living room to upstairs. Used to be on Ethernet, but now on wifi. That used to work just fine and there are no changes, yet... it will logon on the router, but not on the internet. Laptop works fine on the same network, so does my iPod Touch.
Used the assistant, to no avail. Did a full hardware check (just in case).
Deleted the network and added it again.
So far nothing. Logged on the network and that's where it seems to...