here, this is the method I found that is supposed to remove the memory hack. I saved the URL but lost it when favorites got rearanged.But I went arround and tracked it down to see if it would work for you. I'll try it myself when I have the time.
Go into the section "Repairing a hacked MP3 player" and you should be allright.
Repairing Counterfeit Fake MP Players SOSFakeFlash