ok updated with your files, the blank screen is gone now and he shows me a error. Now also the Login
window shows up.
Warning: usort() expects parameter 2 to be a valid callback, no array or string given in /usr/www/users/medihi/medihimal/piwik/core/View.php on line 212
Backtrace -->
#0 Piwik\Error::errorHandler(…) called at [:]
#1 usort(…) called at [/usr/www/users/medihi/medihimal/piwik/core/View.php:212]
#2 Piwik\View->render(…) called at [/usr/www/users/medihi/medihimal/piwik/plugins/Login/Controller.php:105]
#3 Piwik\Plugins\Login\Controller->login(…) called at [/usr/www/users/medihi/medihimal/piwik/plugins/Login/Controller.php:65]
#4 Piwik\Plugins\Login\Controller->index(…) called at [:]
#5 call_user_func_array(…) called at [/usr/www/users/medihi/medihimal/piwik/core/FrontController.php:117]
#6 Piwik\FrontController->dispatch(…) called at [/usr/www/users/medihi/medihimal/piwik/core/Plugin/Controller.php:741]
#7 Piwik\Plugin\Controller->redirectToIndex(…) called at [/usr/www/users/medihi/medihimal/piwik/plugins/CoreHome/Controller.php:57]
#8 Piwik\Plugins\CoreHome\Controller->redirectToCoreHomeIndex(…) called at [:]
#9 call_user_func_array(…) called at [/usr/www/users/medihi/medihimal/piwik/core/FrontController.php:117]
#10 Piwik\FrontController->dispatch(…) called at [/usr/www/users/medihi/medihimal/piwik/index.php:62]