a500 tablet

HI Try Hard reset with a paper clip first if tablet is not responding.

You need to power on thetablet insert the paper clip in rest hole and hold it for few seconds,tablet will vibrate and will come back to normal position.

If that doesnt work you need to try factory data reset.which will wipe out all the data.

Power off the tablet.
Press and hold the Volume up button, which is located closest to the rotation lock.

Note: In landscape view, with the volume buttons across the top of the tablet, Volume Down is the lefthand button. In portrait view, with the volume buttons across the right side of the tablet, Volume Down is on the bottom.

With Volume up button held, press and hold the Power button for 3 seconds then release it. Continue holding the Volume up button.
Once the tablet vibrates, switch the touch screen lock switch on and off repeatedly while still holding the Volume up button.
Release the Volume up button and stop switching the touch screen lock switch once the "Erasing Userdata..." message appears in the upper left corner of the screen.
Once complete the tablet reboots and starts with the OOBE screen, at this point the tablet will have been restored to the factory default settings.