If no products are available to purchase in your event then you have not added any products to the Price List which is attached to the event. To correct this problem, make sure you click the check box to the left of the product names you want to include in your Price List when adding or editing one. You can add or edit a Price List here:
Event Proofing Controls > Manage Price Lists > Edit/Delete Price Lists > Edit button next to the appropriate Price List > Click the checkbox next to the products you want to include in the Price List