Is it possible to use the PC for Fortnite?
Why are you asking this here? You gave the hardware, then you just googlest yourself according to the system requirements and compare!
You can try it, but I doubt it works. If you're thinking about upgrading, it would be better to buy / build a brand new one.
A 360 euro PC is better than that
Will not run very well because the GTX 660 represents the minimal in graphics performance.