Will not turn on after screen replacement!

I've replaced another screen recently and this hasn't happened, i did the same thing to replace a cracked screen and once everything was done, before closing, i tried to turn it on and nothing would happen. Ive tried the battery short, the screen on another ipod and works, all the cables look perfect, i've tried plugging it in, hard reset, plugging into the computer, and same thing. Nothing! can anyone help me please?