I have an asus motherboard i want to use...

Remove the case and use a flashlight and look at the circuite board, there is usually a number on it that is the model number, its usually in big letters.

If you look closely, most boards will have small text identifying what the parts are. the Pins for the power button and USB are usually labeled.

Sometime you just have to guess on the pin set up. usually the pin letering faces avay from the board and goes from left to right.

on the board in tiny letters it might say PWRLED for Power button LED, HDD for hard drive light, PWRBTN for the power button, RST or RSTSWTCH for the reset button and there will be a spot where ther is a pin, a space, and another pin. This is usually where the system speaker goes.

Hook up the board with poer and processor and a hard drive and then try the pins until you get it right. They shouldnt cause damage to the board if you get it wrong as they are low voltage. Its up to you to try that or try to find the schematics.