iPod(4th) wont power on, will not charge, and not detected by iTunes.

I recently went to repair my girlfriends ipod screen which was broken. Bought a screen online on amazon, and replaced the screen and closed the phone back up.

Once turning on the phone, everything worked fine with the LCD, but sadly the touch screen was not working at all and not sensing my touch.

So, i figured there was a problem with the screen, sent the screen back in to amazon and said it was defective, and bought a new one...once I plugged in the new screen to the logic board, and tried powering the phone back on, nothing happened.

I then plugged the phone into the wall, and again, no power. (yes the charging cable is working as it works with my ipod.)

Plugged into my pc with iTunes up, and its not detected. (also tried 2 other computers and used my ipod with my current computer, so its cant be the pc)

I try seeing if putting the device in dfu mode does anything, still not detected.

Tried the home+power button for 30 seconds, also no response.

I read on here that a possible solution is to ground the positive battery terminal to the ground, so I detach the charging cable and re-open the phone and try this, and still no power or detection by itunes. I also read that it could be a trip in the logic board and all i would have to do is leave the ipod be for 3-4 days and let the battery completely drain before charging. I did this and nothing worked.

I am wondering if the problem is a messed up battery or logic board or something else. I checked all ribbon cable connections and all seem to be working properly. Currently i do not have a voltmeter to check the voltage on my battery, but would like to know if there is any other process i could do to narrow the problem down. If the problem is the battery, i do not have a soldering kit to repair it, so before buying a voltmeter, battery, or a soldering kit I would like to expend all other options.

Thanks for any help you can offer :)