Q: can't access airport extreme with Airport Utility

Reset the AirPort Extreme >  Resetting an AirPort base station FAQ

Then see if it's recognized in AirPort Utility.

If your AirPort Extreme looks like the round or dome shaped product in your avatar, Apple discontinued support of this product over 3 years ago when they introduced the Lion operating system.  So, it won't show up in any recent version of AirPort Utility.

Is this a possibility?.....or.....are you asking about a different version of the AirPort Extreme?  If yes, the model number would really help  us.