In Internet Explorer 7 click on the 'Tools' button located in the upper right part of the screen (next to the gear icon) and select 'Internet Options'.
Click on the 'Security' tab and then click on the 'Custom Level...' button.
Scroll down until you can see scripting. Its located near the bottom of the list. Set the option 'Active scripting' to 'Enable'. Then click on the 'OK' button.
You will be asked if you want to change the settings for this zone, select yes. Close your browser and try browsing ads again.
In Firefox click on the 'Tools' menu and select 'Options'.