Some people say pressing the reset button/hole will work, others say your tablet asks for your Google password afther 5 tries. But unfortunately, non of them works.
The only thing you can do about it is a factory reset, this means you've to delete all of your data (including the password you set).
Step 1: Turn your device off
Step 2: Turn your device on, by holding the power button.
Step 3: When the screen lights up, release the power button and press and hold the volume up button.
If you've done this right, a blue area with some text appears on the top of your screen. Follow the steps shown on that screen.
DONE! YOUR DEVICE IS NOW READY TO BE USED AGAIN!
Now, just a tip:
If you don't want to lose your data again, go to Settings → Back-up and reset → Check the boxes and set an account.
If this feature does what it says, you won't lose your data if you do a factory reset again.