Probably the update wasn’t complete and some files are missing.
If you have FTP access, follow these steps.
- Download you
wp-config.php
and save it somewhere. - In the wp folder on server delete everything but the wp-content folder
- Have a DB backup, if you can
- Download from wordpress.org the zip of wordpress and extract it
- At this moment remove the
wp-content
folder from the extracted zip - Also remove the
wp-config-sample.php
and put there yourwp-config.php
- Via FTP, upload to server all the files
Now it should work, but probably you have to change hosting…