If you don't mind factory ressetting try this (BEFORE DOING THAT CHECK IF YOU CAN COPY YOUR DATA FROM INTERNAL STORAGE TO YOUR COMPUTER USING THE USB CABLE WITH THE SCREEN LOCKED, AND DO IT. WHEN YOU WIPE PROM SETTINGS IT SAYS THAT IT ERASES PHOTOS (SO I THINK IT ERASES INTERNAL MEMORY)):
Turn off the tablet, I think you can do it from the lockscreen, if it doesn't work press the power button for a long time.
Turn on the tablet holding volume down and power until some text appears in the bootloader screen.
Then wait for the tablet to ask you to confirm what you want to do before 10 seconds (boot android or wipe data).
I don't remember if it was volumen down or volume up, anyway don't worry it appears on the screen. One of these buttons will allow you to choose what you want to do. The other will confirm what you've chosen. Remember to do this last thing in less than 10 seconds or the tablet will boot android normally.
I hope you can wipe this way without having to enter the pattern.