i think you;ll need to contact the host for help on this one.
trying to access the File Manager CSS File:
/webassist/kfm/themes/webassist_v2/css.php?uicolor=%23eee
is giving a 500 server error message. this is a generic error message that is used to mask the real error, we need to know what the real error is, but I don't see an error log. Something on the server is preventing the File Manager CSS to load properly, this is why the file manager window does not look right.