Are you using expandable memory? If so you may just have loaded too many songs on and it is just running slow. That would be the normal problem. I mean the obvious solution would be low battery, but I suspect you have tried that. Well that's the best I can do. Hopefully someone else can come in here and help you out. Good luck!
I have a Sansa E250 and have loved it ever since I got it, but it is running really slow. I downloaded the newest firmware and it slowed it down a lot. It takes about 30 seconds just to make a song play. If anyone has some suggestions they would be welcome. Here is my MP3:
http://www.circuitcity.com/ccd/productDetail.do?oid=193560&om_keycode=4

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