6
1. Copy the content of the htdocs/ folder where it can be accessed by your server
2. Ensure mainfile.php, cache, templates_c and uploads are writable by the webserver
3. Access the folder where you installed the htdocs/ files using your web browser to launch the installation wizard
So you have done these and run the installation wizard...Have you checked the FAQ section on blank pages to see if there is anything there you may have missed?
And since it is 2.0.15 did you try this:
Revealing the blank page backtrace log
XOOPS displays a basic error page when a fatal error preventing it to run is encountered. To help you diagnose the cause of the error, this page contains additional messages that are hidden by default. To reveal them, use your browser "select all" function (for most browsers, you can use "Ctrl+A").
Let us know how you get on.