Won't turn on or appear on iTunes

I've replaced my friend's iPhone 5c in the past but over time the LCD separated from the frame and just completely stopped working and so I had to replace it once again. However the screen did not seem to turn on and when I connected the phone to my macbook, it just vibrated constantly and then I unplugged it and plugged it again and now the phone overall does not respond at all and does not appear on iTunes at all. I've been using a genuine iPod cable this whole time also so I'm just really confused as to how this could have happened. Please help, thank you!