This site is being deprecated.
Please see the official X‑Plane Support page for help.
Please double check that you have the correct disc in the drive and that they are not out of order. Unfortunately, the installer is not smart enough to know if the wrong disc is inserted when it asks to change them.
Do you have access to any other computers to see if this is a consistent issue? You can also try downloading a copy of the installer from the X-Plane website, unzipping and launching it with DVD 1 in the drive to see if that gets you started. Uploading a copy of the installer log.txt from the desktop might help as well.
This site is no longer being actively maintained.