You lost me somewhere. Do you get the Internal Server Error when you try running Kickstart in your site's root or the subdirectory?
In any case, a white page or a page with a 500 Internal Server Error is, in fact, either a .htaccess issue to a PHP fatal error in disguise.
First, let's see if it is a .htaccess issue. Try renaming the .htaccess file in your site's root (the parent directory to your subdirectory) to htaccess.bak If that solves the problem, the issue was with a directive in your .htaccess file. We'd like to recommend you to try removing directives from your .htaccess until you find the one which causes the problem.
If that doesn't help, the error you are receiving is in fact a PHP error in disguise. First, check your server's error logs (not the access logs) immediately after visiting the page which throws the error. There should be an exact description of the PHP fatal error which occurred. Sometimes you can find the error messages in files called error_log or error.log inside the directory Kickstart is in. If unsure about the error log location, please consult your host. Most likely the error logs are available in your site's cPanel, Plesk control panel or similar hosting account management facility. Try accessing Kickstart, immediately go to the error log and copy the PHP fatal error message here.
If you still get a white page, edit the .htaccess file in your site's root. If you don't have a file named .htaccess create a new one. Beware that htaccess.txt is a
DIFFERENT FILE and will NOT work! Add the following to the end of the file:
php_flag display_errors On
php_value error_reporting 32767
and retry loading Kickstart. Once you get the error message, copy it here and remove those two lines from .htaccess.
If none of these methods work, we're stuck and it's impossible to debug this issue. In this case you can try the scenic route. Extract the backup archive locally using Akeeba eXtract Wizard. Then upload all extracted files to your site's subdirectory. Let's say that your subdirectory is called
test. Now visit http://www.example.com/test/installation/index.php with your browser, where www.example.com is, of course, to be substituted with your site's domain name. If the restoration page doesn't come up we're stuck. Most likely there is a conflicting .htaccess directive in your main site's .htaccess which doesn't allow the files in the subdirectory to be accessed or the permissions of the uploaded files and/or the directory you created cause this issue. In that case try giving the directory 0755 permissions. For all of its contents, give its directories 0755 permissions and all files 0644 permissions.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!