Check the network configuration.
Airport Utility 6:
Open Airport Utility, select your Airport Extreme and click Edit. Navigate to Internet tab and check Connect Using, it should say DHCP, also see if the IPv4 Address is valid. Go to the Network tab and make sure Router Mode says DHCP and NAT. If any changes were made, click Update on the bottom right.
You might want to consider trying a Factory Default Reset on the AirPort Extreme and then configuring it again using different wireless network names, device name/password and wireless network password(s).
If any of your Macs happen to be covered by AppleCare, the AirPort Extreme might quality for replacement if it does not behave in the future.
Try changing the radio channel of the wireless network.
Airport Utility 6:
Open Airport Utility, select your Extreme and click Edit. Navigate to the Wireless tab and click Wireless Options. Change the 2.4GHz channel to either 3 or 9, then Update.
Airport Utility 5:
Open Airport Utility, click Manual Setup below. Navigate to the Wireless tab and change Radio Channel Selection from Automatic to Manual. Then click Edit, and for 2.4GHz choose 3 or 9.
If all else fails, change the wireless network name and have all devices and computers reconnect to network.
Having the same problem - got a range of (all Apple) devices and two Airport Expresses - they tend to come on and off but not a reliable connection - for instance WiFi backups from phones and Gen 1 Apple TV are not working properly/at all, although strangely we can all get to the internet (I am right now) just like the original post.
Exact same thing is happening here... Did a hard reset, have setup the base station from scratch, all OK. Internet (wired, 802.11G and 802.11N) works as a charm, but I can't connect to my Airport Extreme anymore through Airport Utility app (version 6.1)... The whole thing started here because the Extreme was flashing orange/amber continuously. So I wanted to check Utility to see what happened, but wasn't able anymore to connect to it; it kept asking for my password, without actually going somewhere and then suddenly it said that the device is not found any longer. I really can't make anything of it...
I've been having the same problem. I got a new DSL modem a couple months ago and changed my network from bridged mode to a non-bridged mode where the Airport Extreme (AE) is handling DHCP. Since then my wifes 2009 MBP is working fine, but my 2010 unibody MBP sometimes can't connect to the AE through the Airport Utility (AU). (Both computers have the same AU version 5.6.1 (561.3), and the same network configuration.) Normally, I just unplug and re-plug-in the AE and then I can connect to it with AU. The connectivity is getting worse, and today I still can't connect after unplugging and re-plugging-in. Of course, this means that I can't backup using Time Machine, or print using my network printer--all very strange since I'm obviously connected to the network and can surf the Internet (although 2 days ago I was having trouble staying connected to the Internet, which was unusual--again, my wife's computer had no problems). In fact, the network info says I'm connected to the Airport Extreme!
Card Type: AirPort Extreme (0x14E4, 0x8D)
Firmware Version: Broadcom BCM43xx 1.0 (220.127.116.11.4)
Country Code: CA
Supported PHY Modes: 802.11 a/b/g/n
Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 132, 136, 140, 149, 153, 157, 161, 165
Wake On Wireless: Supported
Current Network Information:
PHY Mode: 802.11n
Country Code: CA
Network Type: Infrastructure
Security: WPA2 Personal
Signal / Noise: -59 dBm / -94 dBm
Transmit Rate: 117
MCS Index: 14
I suspect that all of us having this problem also notice that it clears itself up in a few days or so. Last week I was expecting I'd need to replace the Airport Extreme, but now all is fine again. It even connects to my iphone and ipad so they show up in itunes!
Could it be some software glitch in Airport Utility?
I also found that Airport Utility will fail to find it if I have my cable modem ethernet plugged into the iMac ethernet port. As I looked around in Airport Utility, I found a new choice had appeared within the "Other Airport Base Stations" in the main screen top left that gave me the option to search by wifi or wired. When I clicked on wifi, it all of a sudden found the Airport Extreme again. This choice does not exist when I'm connected by wifi, and I never thought to look at that before.
So, there may be other undocumented things going on in Airport Utility that are contributing to this "disappearing airport" problem.
I'm glad it's not hardware.
I unplugged my airport extreme's power cable to powercycle it but all the lights still stayed on. Freaked me out for a minute. Found out it was leeching power from a powered USB hard drive dock I had plugged into the USB port. Once I disconnected that too the lights finally went out. Plugged the power cable back in after 10 seconds, it came back up and all was normal. Don't know what caused this.
Anyone found a solution. I'm having similar issues. A second Mac that is exclusively wireless has not been able to print for several months. Can't figure out why. Recently I just discovered that it airport utility (ver 6) it shiw a globe a green light for connected to Internet. My time capsule is not showing nor is the airport express that extends network. In fact it comes up with message can't find anything! Also no time capsule backup has occurred on this machine since December. I may have done a hard reset then to solve an issue I was having with security.
I suspect I can't print since I can't see the time capsule and new airport express. Why can I not even see the other devices on this machine?