Chosen Solution
I have brought an Imac, and it’s fans start spinning and diagnostic led’s 1,2 and 3 are on the 4th one isn’t no display but machine running?
Sadly the GPU logic has likely failed (soldered on ATI Radeon HD 2600 GPU) or the high end offered a GPU module. Or the LVDS cable connection to the display has become damaged or the LCD display its self. A used replacement logic board goes for $60 ~ 80 USDA used GPU board 2007 (2.6GHz and 2.8GHz models) $150A used display is about $80A used LVDS cable is about $12 Without doing more diagnostic work I’m only guessing.
