4.5 Update-Admin Page Problems

Hello,

I’m a beginner, and I am working on an intranet site for work.
I updated to 4.5, and I had a couple issues. First, I tried the one-click update, and this is what it said:

Unpacking the update…Verifying the unpacked files…Preparing to install the latest version…enabling maintenance mode…copying the required files…disabling maintenance mode…Could not copy file:wp-includes/images/w-logo-blue.png…Installation failed

After that, my site had a 500 error and nothing would show up in any browser. I uploaded a fresh wp-includes folder through FTP, and that fixed the outward facing, but now my admin page looks crazy and I can’t navigate to anything: https://imgur.com/JGnNS8A

Here’s what I’ve tried so far:
Manually updating all wp folders
Changing .htaccess file name
Increasing php memory in wp-admin folder
Confirming that wp-admin folder has css files
Manually deactivating all plugins
Removing Tesseract theme and activating 2016 (default)
Emptying browser cache
Opening on Chrome, Firefox, IE, and mobile (iOS)
Restarting server

I put the Tesseract theme back so that people can still view the website normally, everything on the outward side works fine…links, buttons, everything, in all browsers mentioned above. It’s just the admin page.

I would like to avoid reverting back to the old WordPress version…I have a backup but it’s not the latest design (my fault I know, rookie mistake that won’t happen again).

Any insight or ideas on how to fix this would be greatly appreciated!