If your system is able to play a song that isolates the issue to the video.
You stated you also plugged in an external monitor and nothing was seen on it. That isolates the issue down to the video card as the GPU card feeds both the internal & external displays data signals.
Follow this IFIXIT guide: [guide|6272|iMac Intel 21.5" EMC 2389 GPU Card Replacement]
If your system is able to play a song that isolates the issue to the video.
You stated you also plugged in an external monitor and nothing was seen on it. That isolates the issue down to the video card as the GPU card feeds both the internal & external displays data signals.
Follow this IFIXIT guide: [guide|6272|iMac Intel 21.5" EMC 2389 GPU Card Replacement]
If your system is able to play a song that isolates the issue to the video.
You stated you also plugged in an external monitor and nothing was seen on it. That isolates the issue down to the video card as the GPU card feeds both the internal & external displays data signals.
Follow this IFIXIT guide: [guide|6272|iMac Intel 21.5" EMC 2389 GPU Card Replacement]