Tablet showing 0 internal storage even after flashed
Disclaimer - I don't have enough reputation to place comments - so here is a suggestion.

I have been looking around and found a blog from a user with the same device who has rooted it successfully here.
Plus the comment from a user here.

I suggest to get your device rooted and then install (clear some temp files before installing if you can) the disk utility from here

From the app, you can see where your data is being used.

PS: You don't necessary need root privileges to get this utility working. However, I am presuming you have flashed the device perhaps to death and may have lot of old data which may be stored from within the system data part of your Android device.