Does not turn on when plugged in after screen replacement

Hey guys, was wondering if I could get some insight on a recent problem.

I have an iPod 4th gen 32GB which I got from a friend 1-2 years ago, and today I attempted replacing the screen. To my surprise nothing happened after I put it all together. I wonder if the version it was in has something to do with it. Anyway it won't turn on, won't charge, won't be recognized in iTunes and noting happens when I attempt to put it in DFU mode. I tried grounding the battery terminal and nothing happened. I think that all cables are attached and nothing is loose. Any suggestions?