I can tell you what just worked (and didn't) for me in an all Mac system. I have an Xtrme as the base station and an old AE (pre-n) next to my stereo. Sometime after the update to iTunes 10.5.2, things stopped working. AirPort Utility showed the AE on the network with a nice green light, but trying to connect to the AE from iTunes on my iMac, I got a "connecting" popup that lasted about 20 seconds and then disappeared, with no error message.
1) I tried a reset of the AE following some previous suggestions. The result, flashing amber and the AE no longer appeared in AirPort Utility. This was worse than before the reset in some regards.
2) I brought my AE close to my Xtreme and connected by ethernet. I now got the AE to appear in AirPort Utility, but the light was still amber, not green, both in the Utility and on the AE.
3) I then selected the AE and clicked on "Manual Setup," but that ended in an error message about a DHCP conflict, and the AE disappeared from AirPort Utility. I did get a message that I might like to try again.
4) I unplugged and then replugged in the AE so that it would appear again in AirPort Utility. (Rescan might have worked, but that's not what I did.)
5) This time, I clicked on "continue" (to change settings on the AE). AirPort Utility told me I had a profile, and I answered about 5 questions to accept the current profile settings. And now it works.
It's all alchemy to me.