First off, I'm not a computer expert in the slightest. However, I do know some of the most frequent fixes to these kinds of problems. So, try some of the following possible solutions
- Reinstall Fortnite. A file might have been corrupted or something could simply have gone wrong during the installation. Reinstalling the game should fix this kind of issue
- See whether you have installed the latest graphic drivers
- If you have it installed, delete GeForce Experience. This program from Nvidia is used to update graphic drivers, but is known to cause a large amount of problems. It's best to simply download the latest drivers from the nvidia site directly and install them that way
- Seeing how you mentioned you've just bought a new pc it is unlikely that this is the case, but check whether your windows is up to date
- Try running the game as administrator
I hope any of these worked. If they don't, plese tell us so, since the solution might be a bit more complicated (but there's always a solution :D )
Cheers!