Dead G5 - reset PMU?

I left my G5 on overnight and this morning it is not working. The power button will light up only when I hold it down but there is no sound and nothing else happens. Then as soon as I let go the power button, the light goes off.

I think I need to reset the PMU (or SMU?) button.

But - where is this button? I opened the G5, took out the plastic deflector but am not sure where the PMU or SMU button is. Do I need to remove the fan assembly to get to the reset button? If so, how do I remove the fan assembly - does it just pull out?

By the way, I have a Power Mac G5 produced in Oct. 2004.

Thanks for any advice! I am hoping it can be fixed without a trip to the store.