Can't get iPod to turn on after screen replacement

Just replaced the screen on an iPod Touch. I was extremely careful not to tear any cables, and everything went back in its correct place. Never had any problems before. However, I cannot get the ipod to turn on - it stays on a black screen no matter what I do. I've tried re-connecting all cables, and i've tried grounding the 3.7v terminal as suggested elsewhere. My PC does not acknowledge the device whatsoever. Have tried DFU mode, but still doesn't show up in itunes. Also tried hard reset.