There are plenty of things that you can check: whether ALL CKEditor files were copied correctly (including the skins/skin_name/icons.png file), whether the file permissions are OK, whether you do not have any spelling mistake in the skin name or some file paths in your configuration...
Re: Missing images button
Documentation Manager, CKSource
See CKEditor 5 docs, CKEditor 4 docs, CKEditor 3 docs, CKFinder 3 docs, CKFinder 2 docs for help.
Visit the new CKEditor SDK for samples showcasing editor features to try out and download!