Joomla Administration page is blank after upgrade
You've gone to log into the admin side of your Joomla! 3.0 website and you are confronted with a white blank page. Normally when you get an error on a Joomla! website you will actually get a display on the screen of what the error is. If it's not showing you the error then it's very difficult to work out what's wrong. I found a very simple fix for this problem.
In order to see the errors, you need to go to your configuration.php file in your control panel. Open the file in edit mode and look for something similar to $error_reporting = 'default';. All you need to do is replace the "default" with "6135" (minus the quotation marks). When you go back to your website the errors should appear after refreshing the page.
I can't help you with your error because every case will be different. However, I can tell you the problem I had which may indeed help you. The error that appears on the blank page will probably not mean a lot to many people. However, if you look at the very end of the error code line it will give you the path to what may be causing the problem. With me, it was as simple as going to my cPanel, going into the plugin folder, then the user folder and deleting a PHP file that was related to Jomsocial. It was probably due to the fact that I did once have Jomsocial installed on my website. I uninstalled it because it wasn't used, however for some strange reason after one of numerous website upgrades, the file that was left was causing a conflict somewhere.
It was a very easy fix for me, I hope it is for you as well