Use FireFox and turn on WebDeveloper tools/Console.
See if you can get to that screen again.
What you should be seeing is something new and, IF I re-call correctly, first made appearance in 3.2 or 3.3 of Moodle. Looks something like below:
Have to open the dialog box where one can enter a password - the pencil and eye icon. Your screen, obviously, doesn't show that.
You made reference to 'only thing different' being IIS and PHP 7 ... so that means you've been successful installing 3.4 using Apache on Linux with PHP 7?
PHP 7 but what version? Have all the required PHP extensions?
Could you add Section 7 lines for debugging to config.php file from config-dist.php?
You might have to copy config-dist.php file to config.php and then manually add variables for what would have been generated by the installation process to get back to the screen that finishes the install ... that of creating an admin level account.
'spirit of sharing', Ken