iMac black screen death after everything. All 3 led diagnostics on

I have 21.5” iMac late 2009 model 1311. When I bought it it was with incomplete os installed till disk utility.

1 Internal display Was work Ped

2 external display was worked

3 usb bootable worked

4 Half installed OS X till finalise setting screen

but facing 3 problems

1 dead pram battery

2 late start button response

3 Mac hdd show multiple error message while OS X installation.

After replacing same model number pram battery.

1 Display stop working. Internal & external.

2 usb bootable stop working.

3 I replaced new display lcd cable, pram battery & vertice synchronised cable.

4 mac hdd showing multiple errors that is why I make partition through trans MAC software through windows.

5 tried new hdd also with clone method and bootable usb method.

6 all 3led Diagnostic light working.

checked every cable. Confused about lvds cable face orientation but tried all possible directions.

7 try prm reset, safe mode, options to boot, bootable, external display, another Mac OS clone via usb hdd, f1 f2 brightness, heat sink for processor & graphic card, almost everything.

8.replace broken old vertical syn flex cable also.

9 checked Lvds housing port.

10 Checked psu volatge

11 Try hdd thermal port for lcd panel

12 LCD lvd power supply voltage

13 Power cable checked.

14 use signal 2gb ram

If showing all 3 led all means everything working fine why not at lest external display work. Is this model has removable graphic card

current stage

1 Imac work

2 start sound & chimp sound work

3 fan work

3 led diagnostic light work

4 No display internal external

5 With & without iMac start with chimps sound, start sound, led 3 on-board lights

6 Broken thermal lcd socket pin housing at the time bought

7 Without Hdd it at least show white screen but no

Doubts

1 wrong Lvds cable orientation both to logic board and LCD screen.

2. Same Model New but not allowed to boot.

3 Problematic HDD

4 Does new lvds and vertical sync cable create problem.

please help

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