This is just about parr for the course for me for the last few days. 3 of my sites have issues I can’t seem to resolve, so I shouldn’t have been surprised when the usual WordPress update came along and my admin panel went blank after an update failure.
I have had this in the past and got the ‘maintenance mode’ error, so I went straight away and deleted that file in the root folder.
All of the wp-admin pages just showed up blank, no error messages. The login page worked, but after logging in everything went blank.
Strangely enough the site itself, this one, worked fine, but I was unable to access the admin control panel to do any troubleshooting.
If this happens to you, it really is a pretty simple fix, but it will involve re-uploading a new install of WordPress.
Download the latest version (do this again, even if you just did it) to make sure you have the latest and uncorrupted version.
Just go in via FTP and rename the wp-admin and wp-includes folders (I usually just append -OLD to the folders).
Then FTP all of the files except for the wp-content folder in the new WordPress install folder into the folder where your wordpress install resides.
You can do the others from the wp-content folders separately. I usually do them individually since I have my sets of plugins and themes that have been tweaked.
Then go to yoursite.com/wp-admin/upgrade.php and you should be okay.
I hope so anyway.