ok go into your time capsule, did things change in it? is it back to it's factory settings? When I did this, when I attached the airport exp to the network the time capsule was creating, the time capsule reset itself. I had to go back into time capsule and reenter in all the stuff for it to work. Keep playing with it, and making sure everything is set up right even after you've set it up. double check everything.
on another note there was a firmware update for timecapsule recently which might have fixed any irregularities.
First sorry for the spelling I am dislex......
I did not have a problem but I move home and the new ISP gave me a new Modem/Router and now I have the same sort of problem but have made some discoverys that might help diganose and fix the problem.
I have one Airport Express and Wireless Router/modem. The AE is in another room to the router so I setup it to join my wireless net work and use airtunes from iTunes to my HiFi and connect to a mediaplayer for films using the ethernet from the AE. This works until I stop playing music then the AE disapears from iTunes and the AP utility but I can still ping it and access the Mediaplayer.
Well today I was looking round the menus in AP Utility and found "File - Configure Other" I cliked this and it asked for the address and password (as I set a static IP) I entered the IP and Password. The information appeared I changed one of the fields and changed it back again so the update button become avable and updated the AE. It then appared in iTunes and the AP Utilit. I appears that Bonjour loses the link from name - ip and this is the problem how do I fix it? (perhaps its a DNS problem I can setup a local DNS on a server but do I relay need to do that to get this to work again?)
P.S. after typing this I tryed again and I had to power cycle the AE this time :-(
In case this is of any use to people - I had this issue and fixed it. I know this in an old thread, but it was the best fit I could find.
Symptom: two Airport Express boxes (older ones) that I use only for wifi audio streaming in different places in the house. One gen 2 Apple TV. One ASUS "Dark Knight" RT-N66U router. Router works perfectly with most devices, laptops, phones, and the Apple TV.
The Expresses, though, recently started this behavior: power on, they join the network for 5-30 seconds, and are visible to my Mac with the Airport Utility and in the router's client list. Then they just disappear *poof*. Green light stays on on the Expresses, but I can't see them in Airport Utility or iTunes or Airplay.
I searched all over for a solution to this, and in my case it was DHCP.
Solution: using the browser, in the router config web page for the ASUS router, I located the DHCP configuration. I changed the range of addresses for DHCP to clear some addresses at the base of the range, like 192.168.1.2 to 192.168.1.9, for "permanent" widgets we have in the house like these audio streaming express boxes, leaving the rest of the range for dynamic addresses for phones, laptops, etc.
I then powered off and on the expresses one at a time, and in the short window where they were on the network, used the Airport Utility from my mac to change them from DHCP to a static/manual IP address, then assigned one of the values from that range, like 192.168.1.2 or 3, to each.
From that point on they have stayed available on the network and streaming works. I'm glad to have them back :-)