when i click launch on fortnite, then it’s loading, but then it crashes and then fortnite closes itself
You probably wont get help here as it is AnwserHub dedicated exclusively to UE4. Use fortnite support for help:
For Fortnite issues, please visit http://fortnitehelp.epicgames.com/
There you will find various troubleshooting articles as well as an Email Us button that you can use to get in touch with one of our support staff who can assist you further with this.