It been a very long run with my LG Optimus 3D. To solve problem with stuck preparing storage, follow this solution.
Connect the smartphone/tablet to your PC.
Once connected, turn on USB mode so you can copy/move files from the tablet with your PC.
Once the internal SD card is mounted on your PC, format the internal SD card with your computer to FAT32 with 64k cluster/allocation size.
By using windows command line:
format /FS:FAT32 /a:64K X:
Unmount from the PC. Turn off USB mode. Reboot. You should be good to go.
You can move back your backup files earlier. Better one by one and test. In case there is files that causing the troubles. Good luck.