Answer to "Won't power on or charge"I have had this problem as well, if you haven't tried this yet try to take apart the beats pill and reset the battery by disconnecting it, it will work almost every time unless your beats pill has a short in it somewhere.
Answer to "Why does my beats pill only work when it's plugged up"It is because if you play music or audio while you have it plugged in it will ruin the battery. If you want to fix it what you need to do is take it apart and buy a new battery, but I will warn you that the battery is hard to get to, and you have to carefully move everything inside in order to get to the battery. You also have to be carful of the speakers because they are magnetic and as you remove the tiny screws connected to the battery they will hit it and it can break the speaker. Depending on what type you have will depend on what new battery you get. You can also try to reset the battery to see if that works. I will warn you that most of the batteries I have seen online are expensive. Well, I hope you can get it fixed.