sing a pc with win 8.1 im trying to configure an existing extreme basestation, but utility cannot find airport extreme basestation

For Windows 8, 8.1, or 10, the AirPort Utility for Windows will have two applications listed in the Apps & Features window: 1) AirPort & 2) Bonjour.

• Move or delete the following file from the C:\Windows\System32 folder: dnssd.dll (Note: This is the Bonjour Client Library and is required by the AirPort Utility. If this file is missing would be the main reason you are getting this error. However, even if is present, it may not be properly registered in the Windows Registry. That is, as far as Windows is concerned, it doesn't exist.)
• Download the AirPort for Windows installer. (Note: This utility has not been updated since Windows 7. It will run on Win7, Win8, Win8.1, & Win10 but it will not work with the latest 802.11ac AirPort base stations. It should be fine with the 802.11n models.)
• Run the installer using "Run as administrator" privileges. (Note: If you get the option to Repair or Uninstall, choose the Uninstall option. Allow the uninstall process to complete. The Bonjour application should now be missing in the Apps & features listing.)
• If you didn't get the Repair/Uninstall dialog window, then let the installer install AirPort for Windows in its default folder.
• You should now be able to run the AirPort utility and access your AirPort Extreme base station.

If you have an iPhone or iPad handy, you can use that device to set up the AirPort Extreme.....assuming that it is has reasonably up to date firmware installed.

Post back if you want to try that option.

As a workaround, enter the AirPort base station's LAN-side router IP address in the File > Configure other... menu option on the AirPort Utility for Windows' menu bar.