MM is right. get a new one, they'll charge you probably 100 to fix it. plus the components are usually on one single board so they'd have to most likely order a new part. not worth your time bro. besides, mp3 players and cell phones only have a certain amount of time before they break, a couple of years is a pretty good run for your MP3 player, it's time to let her go.
This may not be relevant, but it solved my problem when I thought my Rio 500 was broken. If you have a similar Mp3 player and are trying to use one of those Duracell Ultra batteries, don't. I noticed that the butt (the negative side) of the Ultra batteries is SMALLER than that of the normal copper top Duracell batteries. The result? The battery isn't long enough to touch both contacts in the mp3 player, thus, no juice.
If this isn't your problem and your batteries really are fine... then I suggest a quick trip to www.ebay.com or www.ubid.com