Pull out the "turbo" card and all the PCI stuff.
How did you turn on the computer before? Check if a power switch is working... (you can use a screwdriver to close the circuit :-D - the power on Mediator, just touch it both pins at the time...).
Do you have any fun connected to power supply? Or listen the HDD...
Check of Mediator is not bended, in my Mediator was some kind of plastic "feet" under which suppose to be laying on A1200 mobo BUT in my mobo I had some chip which make whole Mediator "go up" so I unscrew it.
I'm sorry for English but in some cases my vocabulary is to poor :madashell: