iMac 20 chime loop doesn't post

[Salvatore951]

I am going crazy, I received an iMac 20 2008 that chimes but doesn't post, I mean that iMac chimes but it doesn't read internal or external drive, so I have supposed it doesn't post.
if I connect lcd screen it does chime loop (iMac does chime sound every second and obviously no image)

what I already tried is
1) reflow gpu
2) replaced logic board and cpu
3) replaced lcd

could be the power supply that can't handle the load of machine

iMac first second and third led are on, fourth is off probably because it doesn't post and it doesn't detect lcd

 

[dukefawks]

Reflow.....yeah. Replace the video card.

 

[Salvatore951]

do you exclude the power supply? Are you sure that Gpu is causing chime loop? I don't have this Gpu model now, I should order it on Ebay

 

[Gurmon]

Its the video card.

You already replaced everything else.