If your slider or featured posts widget is not working, try this:
1. Go to your blog dashboard -> Settings and check if your blog is set to Private. Your blog has to be public - the widget uses the blog feed to display posts and when the blog is private, the feed is inactive.
2. If your blog is Public, but the widget is still not showing up, go to your blog dashboard -> Settings -> Other and make sure "Allow Blog Feed" is set to Full or Until Jump Break. If it's not set to Full, the widget can't display posts.
3. If you're displaying featured posts instead of recent posts, double-check if the label is written the same way in the code as it is in your post. Blogger's labels are case sensisitive; for example, if the label is written as Lifestyle in your post, but as lifestyle in the code, Blogger will consider them two different label pages.