There are only two possibilities for SysPrep window to appear by itself when you boot your PC. First, the computer is booted in Audit Mode, in which case you exit Audit Mode as I told in my first post.
Second alternative is that SysPrep is set to to start automatically. I can not understand why because it is not a program you would use regularly. Anyway, check Startup folders both for your user account and for all users and remove SysPrep shortcut if it is present in either one.
Your personal Startup folder is here:
Here are the shortcuts for programs set to start automatically when you boot to Windows desktop using your user account. Remove Sysprep shortcut if found here.
Startup folder for all users is:
Also here remove Sysprep shortcut if found.
Notice that both AppData and ProgramData folders are hidden by default.
If you have exited the Audit Mode as I told you in my previous post, and if you have removed the possible Sysprep shortcut from both locations described above, Sysprep will not open after your next boot. That's 100% sure!