Can you not launch the Photos.app at all? If yes, is there an error message? What is the message? Or is there a problem after launching Photos?
Where are you storing your Photos Library? Is it in your Pictures folder, where Photos is creating it by default, or have you moved the library to an external drive?
The most common resin for not being able to launch Photos at all after a system upgrade is an outdated icon in the Dock. Sometimes an alias on the Desktop or the icon in the Dock are still linked to an older version of Photos, that will no longer run after the system upgrade. In that case try to launch Photos by opening the folder Applications and double clicking Photos there. Can you open Photos this way?