First of all that screw head might totally be the problem, and I am only speaking from the experience of fixing a red dot on an xbox 360 S. Now, I'm going to give you a list of things that may be going wrong. Check the av/hdmi connection (I didn't have it plugged in fully on top of other issues), if that's fine then make sure the fan is acctually spinning when the console is running (do this by running it while the cover is disassebled), make sure that the x clamp on the back of the motherboard is in place fully and settled in its notches, last of all try doing a reflow of all the chips using a heat gun or a hairdryer, remembering to keep the temp. just below 200 degrees farenhiet. Do both sides of the board. Also make sure that all your remaining screws on the heat sink are tightened fully by criss-crossing while tightening. I would definitly buy a replacement screw because even if that's not the problem here, it will definitly cause a problem in the future.