i had this problem too man. i tried reflashing several times but didnt work. i think the flash memory (which stores the firmware) is screwed....
the good news is that probably (if u still have a warranty for it) u can exchange it for a new one at the repair shop. but tell them u accidentally unplugged it while transferring some music. they believed me with that.
oh and make sure it has the same functions as this one. the one i got it as exchange doesnt have gameboy emulator or radio, the other had...