Hi Nicole, thanks so for the detailed explanation.
In my case, the fan power connection is a molex connection. Plug that to the PSU and the 3 fans spin without problem. The Sata connection if for the RGB light on the case front panel button. Both are connected to the PSU. So I have power in all 3 fans, and RGB light in the case front panel button. No problem there.
The issue is with the fans RGB part.
For the RGB part, all 3 fans are connected to a 3x2 splitter (sorry my OP says is 3x1 when is actually a 3x2 splitter):
3 RGB inputs from 3 case fans are connected to this splitter. 2 cables comes out: 1 is labeled as compatible with Gigabyte, and the other is labeled as compatible with ASUS (my mobo is ASUS), Ashrock and MSI.
Then, there is the cable from the case panel. A 4 pin (only 3 with connector pins) male cable. This was factory connected to the 4 pin ASUS labeled cable going out from the RGB splittter. When connected, there s is no RGB light in case panel button AND fans. When disconnected, there is RGB light on the case panel button BUT NOT on the RGB fans.
I will take some pictures and upload here later so you can all see what I mean.
Hope I can solve this, because the case without those 3 RGB fans lighting up looks...not that good.
Best, regards Joe.