Here are, roughly in the order you should try them, some tips that may help you debugging a CKEditor configuration when the editor don't show up in the edit area after you've installed it:
Clear the cache:
Remember to clear the cache after you've changed any setting that has something to do with wysiwyg. Not clearing the cache is probably the most common source for CKEditor not showing up as you would expect.
Check out that roles are configured correctly: