Is it the same connector that the chassis fan of your old case was connected to? And is it a fan with less rpm?
If it spins up at a lower rpm it will not be detected as the same fan in the bios no matter correct the connection on the mobo is
Cheers and good luck,
the fan that i have now has a slower rpm. is there a way to set it so the motherboard detects it?
lmnvum