While disconnecting lcd fan start running rapidly

Hi, I have a problem that fan is spinning rapidly on my mac suddenly when I tried to disconnect my lcd from logic board.

Actually I was trying to disconnect my broken LCD and was trying to get external monitor as a primary monitor so that I can update my Imac to latest OS. But don’t know why my lcd didn’t connect after that and it is not even showing up and its fan starts running rapidly. Could you tell me any solution for this?

Help would be much appreciated.