ony X

Please tell us your system specifications.

If you downloaded the new one (version 2.4.0) you have to use lion.

Here's a link to the Lion download and there are more links down lower on the page.

http://www.macupdate.com/app/mac/11582/onyx

You likely need the right version to match your OS X version.

http://www.titanium.free.fr/index.php

...or more specifically look here on the OnyX download page to download the version of OnyX specific to your version of OSX.