If you are using a large number of plugins, it is quite common to get a blank admin screen after a WordPress upgrade. The main reason is that some of the plugins are not compatible with the new WordPress version.
The easiest solution in this case is to rename the “plugins” folder to something else such as “plugins2” and then create a blank “plugins” folder. After this you should be able to login to the WordPress admin screen. You can then copy one plugin at a time from “plugins2” folder to “plugins” verifying that each of them works with the new version. If not, you can download it directly from either the plugin homepage or from WordPress plugin repository.
Another common reason for blank page after WordPress upgrade is the stale cache files. The earlier solution of renaming plugins should work in this case also. You can also delete all the cached files to see whether that works.
Common reasons for blank page in WordPress admin screens are,
- Incomplete WordPress upgrade – In rare cases, the upgrade process may be interrupted and this can cause blank page problem. The solution in this case is to upgrade again. I usually delete everything under wp-admin and wp-include and then re-upload the same folders from the new version.
- Extra space at the end of plugin files – If there are any white spaces after the closing tag of PHP code in a plugin, it can cause “Cannot modify header information – headers already sent by” error. Unfortunately sometimes this may not be displayed on screen and you will see only a blank screen. You need to be careful with white spaces whenever you edit any PHP file in WordPress. The reason for this problem is that the white space after the code is interpreted as HTML code and would be send to the browser as and when encountered.
- Incompatible plugins – Some of the files you have on your blog may be incompatible with the latest version of WordPress. This could be due to API changes or may be due to low quality plugin code. Either way you need to either upgrade to a new version if there is one or should find an alternative plugin in the WordPress plugin directory.