I have a D915PBL which won't assert the PS_ON# signal to the power supply. I have checked the ON switch signal and the 5VSBY from the supply is OK. I have tried a second MB and it exhibits the same problem. I can temporarly ground the PS_ON# signal and operate the ON switch to turn on the computer. The MB will then assert the PS_ON# to keep the supply on. I can turn off the power with either the ON switch or Windows. Does anyone have access to a schematic as this may help identify my problem?