Despite this being over a year old, I'll still answer it. The device needs to be wiped and the firmware needs to be re-flashed onto the device. I was able to repair a few units with this. The only problem is now, since the Maylong has folded and is not longer in business, the firmware download link is no longer active.
If you were able to do a search and find it, there are two files that can get loaded directly onto a blank micro sd card, and put into the unit before powering on. The device will load the files, wipe the old firmware, and install the new one.