If you have flashed the gmenu2x firmware without backing up and want to revert back. Here is the download link to the original firmware that shipped with the device.Instruction are pretty simple below.
Open your device remove the memorycard
Use Win32diskimager to write the .img file (making sure card is formatted fat32)
Pop back the sd card in the device and boot up.
Source https://mega.nz/#!JIBVDaDa!K1IrPbrjHrdiXQOX9w2b-EAB9n7GHFeQkE084R-cBiQ
link is out please new link please
The file is no longer there unfortunately. Also, I have the 16GB version and all the ROMs have the filenames in Chinese.