A word of caution when reassembling. Be sure to replace the LCD thermal sensor connector and the optical drive thermal sensor connector with the contacts facing down. They are both very small and easy to overlook the contact points. If either or both are reinstalled wrong the iMac will not power up. You will get a white screen momentarily and then it will go black. I made that mistake and had to go back in and correctly insert them which solved the power up problem.