I have locked myself out of my tablet - Proscan Recertified - PLT7035 4GB NAND Flash 7" Tablet

You will need to do a factory reset:

1) Make sure the tablet is powered down.
2) Press and hold VOLUME UP(+) and DOWN(-) buttons, plus POWER button all at the same time.
3) Insert a metal pin in the RESET hole at the back of the tablet, then push and hold it for 2 seconds, while still holding the VOLUME and POWER buttons. Make sure the pin is pushed. It seems like nothing happened, but just keep on going to the next step.
4) Power ON the tablet and immediately, PRESS and RELEASE continuously the VOLUME UP(+) button in order to get the display as showing dead tablet (dead robot).
5) This is the critical part. Make sure you do the right sequence or you will start again from the beginning. Press and hold the POWER button, then press and release VOLUME UP(+), and the display will give you a screen showing different options.
6) Choose the option wipe data/factory reset, by clicking POWER button to scroll down. To execute the selected option, press VOLUME UP(+) button. The tablet will reboot back to its factory setting.