Powermac G4 MDD motherboard ?!

Hello,

I got a G4 to repair: the symptoms where problems with DVD player impossible to open, external hd plugged in in the usb but impossible to appear and many disfunctional troubles

I first opened the machine and found out it was full of dirt so the air couldn't go out nor come in. I so desassembled the whole and cleaned it up.

When I reinstalled everything the comp wouldn't turn on I so looked at threads and found this one :

https://discussions.apple.com/thread/1016371?answerId=4821819022#4821819022

After I did what is written just taking the cooler processor plate and restarted the computer it revived!

I replaced it but the computer is half working, the screen has light on and the leds on the motherboard and video cards are on but the little fan attached doesn't work and no image not sound of good working order.

I tried many things like changing the battery, leaving it 24h as mentioned in the thread upper... nothing seems to revive the motherboard and so can't use it

The strange thing is when pressing the shift key with the power button it shuts down!!! but noone of the keys seems to give any answers.

I tried starting the comp pressing the Alt key and the big fan when mad turning very fast...

that's all about it for now any help? suggestion?

thanks