Start up problem

[diffusion]

Just bought a second-hand iMac G5 20" but it won't start up. when I push the start-up button it shows the power light and after some seconds the fan starts but no sound and the screen remains black.
When hold the power button to off and on it again the fan starts after some seconds but the power light will not shine and the screen remains black.
when i unplug and plug it again the the power light come on and the fan after some seconds and the screen remains black.
I put a HD, but it remains the same. PLEASE HELP.

 

[Hellhammer]

http://guides.macrumors.com/Mac_doesn't_boot

Sounds like the logic board is dead. Contact the seller.

 

[diffusion]

sothing else could be done

Where is the logic Board located? thanx

 

[Hellhammer]

Where is the logic Board located? thanx

It's inside the iMac. Basically, the logic board is the same as motherboard, it acts as a bridge between other components.