Thank you for responding
I just did that and the fans are spinning well .
Yesterday I've read that connecting both of them will be better for the motherboard so fans will get their power from the PSU but I think that is not right.
I just wanted to be sure.
I have bought a new pc case and it contains 2 fans, each one of them has 2 headers (x1 3pin + x1 Molex).
So I don't know if I have to connect the two headers at the same time, or only one of them?!!
can you help
I'll attach an image of the headers