Computer motherboard power managment via embedded device

Hallo,
I want to develop an embeddde device to manage a computers power. To be able to power it off or on and most importantly. I want the device to be attached to the motherboard system so that it cant be detached from the system and incase on tries, there is apower failure and the computer cant start. Am not sure of the computer component to target on the motherboard, so am asking if anyboard can give hand and help me out.
Thanks