The wwwroot check at line 172 of the install.php file uses the fopen() function to open a file via a URL. There have been a number of recommendations that this is a security hole and that this functionality should be disabled (which it can be in php.ini). In addition this doesn't work at all on Windows unless source access is enabled.
This is a brick wall for someone installing an new Moodle system.
Recommend removing or rethinking this check.