iPhone 5 has Black Screen, Vibrates every 12 seconds, PC recognizes it

I attempted to fix my power button, which turned out to not be unresponsive due to a broken Audio Control and Power Button Cable, I ended up replacing it with a new one. Then I put the phone back together and everything looked fine. I plugged the phone into the wall charger to see if it would respond, since that is how I usually turn it on since the power button wasn't working. The phone began to vibrate and make sounds, I could hear the stream of emails and messages, but the screen was black. I went back in to make sure I had properly connected the LCD screen, which seemed fine, but when I closed up the phone the screen was a dark blue color and it began vibrating every 12 seconds or so. I thought I might have not adjusted the LCD screen correctly again, so I went in and now it is only a black screen. I plugged it into the PC and it appears to recognize the phone in Itunes, but not in the computer folder, so I don't have access to photos. I tried calling my phone from another phone but it doesn't ring or vibrate. I know the audio buttons work because I can change from one setting to the next, and the phone will switch between ringing and vibrating; which means it might not be the audio control and power button cable?

What I want to know is why the screen is black, yet the phone keeps vibrating every so often when it is plugged in, yet doesn't vibrate with calls or messages. Does this mean I may have damaged the logic board? or it the screen? I'm afraid of ordering a new screen since they're so expensive and once opened you can't return most.

Thank you for your help!