Olivier Deschamps

You should use Disk Utility to format it.

Hermann, you have a small plastic peg up and down the slot inside the IMac. Did you notice them ?

Jagat, it’s easier if you lift the other side of the display.

Les vis ont des tailles différentes, pensez à repérer où va telle et telle vis.

Are you sure the new HDD is OK ?

The right question is how to fix it rather than why, don’t you think ? Try Macs Fan Control, it should be OK.

Well done Sylvain

Have you OSX installed on your HD ?

Did you plug it on the keyboard or straight from the computer ?

Install Macs Fan Control