Pulled too hard when opening iPhone. Did this kill my iPhone 5 screen?
iFixit has a great guide about the disassembly of the iphone 5. All courtesy of the pictures goes to them. Step 11 clearly demonstrates the ribbon cables . 

I highly suspect that you just yanked a little bit too hard on the LCD cable and hence the black screen. I am in no way affiliated with iFixit but I recommend the use of the iSclack opening tool. It only lifts the screen as much as it needs to preventing you from breaking the delicate ribbon cables.