I think you might have a plugin or theme issue going on there.
Since you aren't able to log in to the dashboard, you will need to go to your site files via FTP or your hosting file manager.
Try manually resetting your plugins (no Dashboard access required). I recommend the FTP/file manager instructions over phpMyAdmin. If that resolves the issue, reactivate each one individually until you find the cause.
If that does not resolve the issue, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue (theme functions can interfere like plugins).