iPod overheats after screen replacement

I have recently replaced my digitizer, LCD screen, and headphone jack in my iPod Touch 3rd Generation. After that, my iPod has been randomly turning off, sometimes the screen will display random lines and a small pop can be heard before turning off. After it turns off, the iPod is usually warm around the lower left region. I've noticed that this only happens when I have my iPod in my pocket or if I squeeze it in a certain way. Anybody have any idea what could be causing this and what could fix it?