Photo does not open files

Try the following;

1 - as a test launch Photos with the Option key held down and create a new, test library.  Import some photos, close and open as a test to see if the same problem persists. Does it? This tells us if the problem is limited to your current library or is more wide spread.

2 - if the problem persists log into a basic admin user account, Set up users, guests, and groups on Mac,  and repeat Step #1. This tells us if the problem is limited to your user account or is system wide.

3 - if the problem still persists boot into Safe Mode according to How to use safe mode on your Mac and open your main library to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

This tells us if there are any 3rd party apps that might be causing the problem.

Now try opening your original library and see if the problem persists or not.