You have not said if the products do not appear in the front end or backend or if you simply get a blank page. When you changed from J2.5 to J3+ (I assume you have J3.6) did you update your Joomla template and any overrides you use?
The first attempt: intstall Joomla 3.6 and Virtuemart 3.0.14 than after copy old virtuemart database ( only product and categories, medias ), copy media files, then reinstall VM, and the categories work, bat not show the product in category. The all product shows in not category view settings, in bulk...
The second attempt: deleted virtuemart, deleted virtuemart database, reinstalled pure virtuemart and i created test category and teszt product, but also not showed product in categories...
This was the point when I started to cry...
