Why does Fortnite crash when I open it?

Since Thursday my Fortnite always crashes and i dont know why. It says:
An Unreal Process has crashed: UE4-FortniteGame
Does somebody know why and how i can fix this?

The AnswerHub is for UE4 questions. Please use the Fortnite support form: http://fortnitehelp.epicgames.com/customer/portal/emails/new

why does fortnite crash when i open it?!?!?!