will not charge past the red bar

hi

I bought my i pod touch from a friend for 70 dollars and it was in acceptable condition and the only thing wrong with it was the screen was cracked and the digitalizer was in need of replacement but it still worked but with the cracked screen it needed a new screen. So my dad and i went on amazon and bought the kit which includes the tools for replacing the touch screen and it also came with the new digitalizer and new touch screen and a screen protector. so i put the digitalizer and screen on the i pod and its just showing a pic of the battery with the lowest amount of charge ,a red bar. what should i do im lost.