This Problem is due to your server environment and not WordPress 2.5.
I found a workaround read below…
Ok so I’m not sure why this is but on my server environment
My Server:
Microsoft 2003 IIs “Shared”
PHP 4.4.7
MySQL 5.0.51
Ok. this server will not recognize WordPress 2.5 in the root or a subdirectory after a fresh install. So I tried everything to get it installed I found a workaround that may work for multiple server environments like my own getting a blank install page.
Follow the steps below:
1)Using FTP or Shell access-Install WordPress 2.3.1 to a subdirectory like /wordpress make sure its a functional Install it needs to be in a subdirectory for workaround. We need the 2.3.1 database to be populated for our workaround.
2)
Following the upgrade instructions
included in the readme.html file with WP 2.5. in the 2.3.1 install subdirectory you created in step 1 above. Erase all files except the wp-config we need this file for the workaround
3)Now FTP or Shell access-all files included in WP 2.5 to the subdirectory we created in step 1 above. Remember we saved the wp-config.php from our prior install of 2.3.1 do not overwrite this file or you will result in a blank install/upgrade page again. If you need to save it in your local machine then reupload it again.
4) Now navigate your browser to https://www.yoursitename.com/wordpress/wp-admin/upgrade.php Not install.php and magically you will see the upgrade.php page. Folow the instructions and WP will repopulate the database with the upgraded tables.
Now your WP is updated and we got around the Blank install/upgrade at the root level. for any of you that want your WP to be available at domain root you will need to copy all the files in the subdirectory and then copy them to root level of the site WP will then be available at https://www.yoursite.com instead of https://www.yoursite.com/wordpress…
Good luck to all WP users who are running into this problem and remember this was just my workaround and may not work for other server environments.