Gerome_1 :
Hi, I am having the same problem. I did a build from my hp-p6754y. I replaced the board with a Asus M5A78L-M/usb3.
There is a 9 pin plug coming from the on/off switch with nowhere to plug it into the Asus. There was a 9 pin plug on the hp. Everything else connected up fine.....Help...Please
This is a common problem with OEM proprietary cases/boards when you try to match them to retail components. The HP case uses a common connector that plugs into a header on the m/b for all the FP wiring. Makes it fast and easy on the assembly line. Maybe something like this will help you go between the HP 9-pin connector and the board's header.
https://www.pololu.com/product/1720