Thanks for the suggestion but we all know how to set the sleep in windows.
The idea is not to found a workaround.
I want to set my streaming computer with a 5 minutes sleep because it is just a fileserver/streaming server and does not need to be up and make heat and noise the rest of the time.
It is automatically awake upon network access when another computer or the Ps3 try to acess it. The prevent Os from Sleep option was perfect for my purpose and i missed it