Here are some possible reasons why your ads do not show.
- When you first paste the code the ads might not show up. They can take a short while to be initialized by Google. Wait a few minutes and then click the "Refresh Page" button. This should cause the ads to display.
- Did you copy the complete code that Google Adsense provided? Try copying and pasting it again (delete the original code first).
- Google has a limit on the number of Google AdSense ads you can place on a page which is 3. If you put more than that, they will not appear.
- Is your site published? Google will not be able to index your site until it is published and this might be a reason why the ads are not displaying.
- Do you have an ad-blocker program installed? Please try disabling this.