M6 SP version does nothing but connect as UMS

I got my M6 fairly recently (December) and it was fine until a while ago. I was copying some files (videos/music) over to the player, and then I updated the music library. I scrolled over to OK, the Miniplayer froze, and then eventually the screen shut off (I think). It can connect to my computer as a Universal Mass Storage device fine, but it doesn't seem to do anything else. I'm not sure if it's even on or not. I haven't tried DFU Tools yet, because when I hold Power + M and plug in the USB cable, it still registers as a UMS device. What's worse is I was just about to sell it, AND I can't return to the seller because I bought it in a brick and mortar store in China.

Any ideas?

Did you load to player some OGGs or FLAC files?

Just some MP3s and XviD encodes (using the bundled software)

That happened to me a few days ago, pressing the arrow button for ~30 seconds worked for me. If that doesn't work, you might need to use DFU tools.

Well, it seems it ran out of battery, which let it turn off so I could start again.

Thanks for all the help though.

Great, so be aware to alwas know, what is your battery status