I have just built a new system, and I am having the problem that when the computer is off, and the power lead is pluged in, the cpu fan, the system fans and the graphics card fans all turn. The hard drive light sudenly lights up too.
When I pres the power button it boots fine, it just takes a couple of seconds before I get the boot splash screen.
I fisrt thought that it was because I had the reset and power switches wired wrong on to the front panell header, but that isnt the case. My motherboard (Foxconn Renaisance) has dedicated power and reset buttons on the motherboard, so I disconected the power and reset button, but the problem was still there?!
In the bios, there is an option to power on automatically after power loss.
There is an option to put computer in standby when power button is pressed.
Check the power options in the bios.