Is your macro security set to Medium? When you create a macro, I believe it
will run right after you create it (but I could be wrong). However, when
you reopen the presentation, if macro security is set too high, you will
not be able to run the macro. Also, macros are stored within presentations
so if you put this in a presentation, it will not be accessible to other
presentations unless you copy it to the other presentation or create an
add-in.
--David

Hej Julien,

which version of PowerPoint do you use? Do you want to use your macro again
for the same presentation it was created in or for another presentation? If
you need to have it available for all presentations, you should consider
saving it as an add-in.

Hälsningar,
Ute