@jwmsales have you tried Bob's suggestion of disabling all your Plugins?
Login to the DB via a DB client like phpMyAdmin or SequelPro. Goto the
{$db-prefix}_site_plugins table and change the value of the
column to
on every row.
Then access the file system and delete the contents of your {$core_path}cache/ folder.
Use a fresh browser—a browser with which you've never logged into MODX before—and try the Manager after those steps.
If the Manager is usable, then you've identified that the issue lies with a Plugin.
If the Manager is still borked then there's some issue with the Manager assets. If the front-end is also borked then the issue is not restricted to Manager assets but your PHP / server config.
Let us know how the above goes...
MODX Staff