Answer to: iPod unresponsive after battery replacementCheck if the receptacle moves on the circuit board or is lifted at all. It shouldn't. Look at the small solder joints and tight space. I watched a video on micro-soldering and decided NOT to try it yet, despite many years building electronic kits and some repair work. A shop estimated $180 while replacement boards or iPods are $40-50. Ensure the new plug is fully seated and inserted correctly. My new batter had to charge via wall adapter, not my computer, for over a day! Hopefully, you got the right battery for your iPod; mine was of higher capacity, but such a long charge cycle surprised me. Also, read all you can and ask for expert help from the place that sold you the battery. I am not a pro at this, just a guy like you with an iPod problem or two. Four days, on and off, and finally mine is ok.
Answer to: iPod unresponsive after battery replacementDespite being very careful, I partially pulled the surface mounted battery cable socket off the circuit board, slightly; not apparant at first, but enough to cause a similar problem. Re-soldering is not possible without special tools. That socketccalles for careful and delicate technique. I used the tip of an X-acto knive, very carefully, to JUST lift the retainer clip slightly; freeing the cable. Also, ensure thsat the cable for the HD is inserted correctly. Reversed, can cause issues akin to the above. View videos at sites like this one.