Tried clearing cache?

Why? Can you see the ads then?

I cleared cache, tried different computers, different browsers.

*bump*

I read somewhere a while back that If there aren't enough advertisers to fill both blocks then the second one will be blank. Could also possibly be some issues if it was added through the scrap book and one already exists on the page.

Have you tried the Google adsense add-on in the marketplace? Maybe that could help?

http://www.concrete5.org/marketplace/addons/google-adsense/...

Features:

Add any type of ad, including: text, images, or both text AND images
Easily change the ad colours to blend with your website. You can change: background, border, title, text, and URL - without needing to know any complicated HEX colour codes
Add nice rounded corners to your ads to help them blend with the rest of your website
Choose from a list of standard ad layouts that will suit any website, including: horizontal banners, vertical banners, square banners, both large and small.
Supports "link units" (a list of keywords related to the topic of your website)
Optionally display ads from an external URL if no Google Ads are available
For advanced users, this block supports the 'Ad Channel' to track revenue from different websites, or different parts of the same website.

See it live here-http://c5extras.com/add-ons/google-adsense/...

Hope that helps, let me know how you get on.