Yes, that story about the 4 pennies under the GPU places I have already read, but I think this was done to increase pressure on the gpu.
In fact, this means that the connections to the gpu was broken and by pressing under the gpu you can "restore" it.
If nothing works, then I could obviously give it a try.
I also read a story that you can remove the harddrive and try booting without it.
These are all premonitions, but so far nobody has been confirmed that this resolves the problem.
Do you know how i can measure the voltage of the power supply to the motherboard? I have a voltmeter with 2 pins.