Here is exactly what I did since the beginning:
1. I installed Megento v 1.4.2 with HelloMinty and it didn’t work because of the upgraded Magento.
2. Backed up the database in magento interface (to save all my products, orders and customers) because I had already migrated them from my previous store.
3. Deleted everything and made a clean Magento v 18.104.22.168 install.
4. Restored the database I saved previously.
5. Installed the HelloMinty theme. (exactly like the instructions)
Maybe when I backed up the database it saved some files of Magento 1.4.2 and then restored them thus causing problems to the theme?