won't charge when plugged into PC or wall charger

if ou have a multimeter, measure the battery (if not, borrow/buy one, even the cheapest one would do the job - my oldest one did cost something around 3$ and that was ~10 years ago - it still works fine)

if the battery is empty (and by that i mean something around 0V) - the iPhone can not charge it. there are other ways to get some power into the battery - but it would always involve soldering and some "special skills" (a.k.a. insanity) - i use a modified gps unit for this job. other use a 9v battery and "shock charge" the empty battery for a few seconds. but that is a little bit dangerous - but it could help to give the empty cell enough voltage to be recognized by the device again - but never ever be lazy and try this while the battery is still soldered to the logicboard.