When your google product feed stops displaying your products you business can suffer. After google changed the attributes which need to be included in the google base product feed some find their products have stopped showing.
To perform a quick fix for this simply make an update of your feed whether using a wordpress plugin or prestashop module so that it creates a new feed, will all your products in.
Then view www.yourdomain.com/en_googlebase.xml
Save the file as en_googlebase.xml
Open in dreamweaver, then use ctrl+f to find and replace:
Save the file then login to your google merchant account and manually upload the file.
Within 24 hours your products should start to appear in google shopping again.