Turn off the compress_js and compress_css system settings. If you can't do it in the Manager, you can change them in the modx_system_settings table in the DB with PhpMyAdmin (change the 1 to a 0).
Then delete all files in the core/cache directory and clear your browser cache and cookies.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html