No disrespect to your Rio but 128meg is pretty tiny these days and, fact is, there isn't much you can fix on subminiature electronics like that, even if you could figure out which bits to replace.
I'd take it as an opportunity to experience a new player -- there are some excellent ones like Sansa and Sony at a decent range of prices.
I have this mp3 player that doesn't retain any of it's settings anymore like the FM station setttings. It started when I plugged it into a 4AA battery box and I'm guessing it fried some component inside, but don't know enough about electronics to know what really went on. Can somebody who does tell me what part got toasted and can it be easily repaired or just tossed out? Thanks in advance for any professional or experienced advice!