My airport is behaving strangely: internet connection on one device, but no connection on another
My airport is behaving very strangely. This past weekend, without any apparent reasons, the light turned from green to amber. As a result, I wasn't able to connect to the internet on my iMac. However, the internet worked perfectly on my iPad; I was able to surf, watch videos, etc.
I opened airport utility and saw that the DNS server(s) were missing. There was a warning that this may cause problems connecting to the internet. I called my ISP and they said they didn't know about the DNS server(s) because the company who makes the router supplies them, not the ISP. I opened the airport utility again, and told it to ignore the DNS server(s). The light changed back to green. But the internet is still not working on my iMac! Which is very strange -- how can the connection work on my iPad all the way to the laundry room in the basement, but it doesn't work on the desktop which is only 1 foot away?
Also, when I connected the Ethernet cable directly to the iMac, the internet worked. So it's not my iMac. But if the airport is damaged, what made it work on one device and not on another?
Any help to solve this mystery and to get my airport back to work with my iMac is greatly appreciated.
10.6.2, airport 7.6.4.