It generally takes 48 hours for Google Adsense to display relevant ads on a site.
But if you have been using Adsense for a while and still see only PSA ads, try this:
1. Type your site URL in the Adsense Sandbox and check the ads for other countries. If you see ads, nothing to worry.
2. If they are still PSA's, check the diagnosis tab in the Adsense control panel to confirm that there's no problem with the site.
3. Nothing works, send an email to Adsense support with a screenshot of your web page displaying PSA.