Newbie Problem - Power Button Bracket, Snapped Ribbon

Hi guys, I am new to the repair thingy and I received my first Pro Tech Toolkit yesterday. I bought that and an audio control and lock button cable to repair my malfunctioning power button. But I ended up not because there's a screw on the power button bracket that just won't budge. I tried extending the shaft, changing screw bits, adding the spanner attachment for more torque, but didn't work.

Also, when reassembling the iPhone 5, I lost a few screws and standoff screws, and accidentally snapped off a ribbon cable located right next to the flash (two screws on the top of the iphone 5, I snapped the one on the right) can you tell me what that ribbon does?

Also, how can I remove the stubborn screw?