Asus Crosshair IV Formula - Manual (Page 30)

5. Power LED
The motherboard comes with a power-on switch that lights up to indicate
that the system is ON, in sleep mode, or in soft-off mode. This is a reminder
that you should shut down the system and unplug the power cable before
removing or plugging in any motherboard component. The illustration below
shows the location of the onboard power-on switch.
When you turn on the ATX power supply, the Power LED flashes three times
to indicate that the system is ready to boot. Wait till the flash stops before you
press the power-on switch.
6. GO LED
Blinking: Indicates that MemOK! is enabled before POST.
Lighting: Indicates that the system loads the preset profile for temporary
overclocking when in OS.
2-4 Chapter 2: Hardware information