Chosen Solution
I was replacing my CPU to an intel i7 870, when I put I back tougher the iMac didn’t turn on. So I put back my original CPU I hear a boot sound but no screen image. I have tried to reset the PRAM and the SMC but its not working! I think I broke the graphics card but I’m not sure. Please help me!
Well the Intel i7 870 is the correct CPU for this series! So unless you got a bad one that shouldn’t have been the issue. Did you remove the GPU’s heatsink by chance to refresh its thermal paste? If not then I can’t see how you effected it. My money is on the displays connections. If you have the system still together lets try this simple test. Place a lit flashlight against the display at a sharp angle are you able to see your desktop and its icon’s? If you are then you know the issue is within the backlight connection or the LED Driver board. If you don’t see a display image then the LVDS cable has become damaged or the logic board connector is damaged. I’ve seen people reverse the connection which will also damage the logic board.
Then the CPU you put in is defective, unless you damaged the LCD connections. This test leverages the Intel internal graphic services of the CPU (not the dedicated GPU) so if that failed the CPU is in question now.
