That should work. Unpacking on top of the distribution is a more or less officially supported installation path. You seem to have confirmed that the files were in the right place.
The cdt version may not match the Eclipse version.
Try Help -> Software Updates... and see if the feature can be enabled.
Try Help -> About Eclipse Platform , then various information buttons there and see if you can find an error or a list of disabled functions. Also check the included list ...
As a last resort, you can try deleting the contents of the configuration directory in the root of eclipse. First back up and do not delete config.ini . Restart with -clean .
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