iMac 20" 2Ghz no boot sound, no video.

[Pragmatiko]

Hello folks,
i have that iMac with no boot sound and no video.
I thested follow parts:
- Graphic Card is ok
- Power supply is ok
- Ram Module is ok
- CPU is ok
- Bios chip is ok
the problem is on logic board.

Any help?

Tks