I spent about 3 hours working on the circuit to try and get a decent 1.2-volt output. I went through several transistors and some trial-and-error. Once I got to a point where I thought I'd see how things were working, I noted that the indicator light on the MP3 player was just staying on. I tried installing the battery but I got the same thing. Oddly, I can connect it to the computer and read the flash memory just fine. Hopefully it'll "heal" if I leave it disconnected for a while.