power on and volume + does nothing

Hi,

Have you tried inserting a opened paper clip or a pin into the reset hole in the back of the tablet?

You will feel a button being pressed as you push the paperclip in. Hold it operated for a few seconds then remove the paperclip, then try to start the tablet in the normal way.

Here is an image of its' location taken from the ifixit repair guide for the tablet. The tablet has been opened but it should be easy enough to locate. The hole and the button switch are highlighted.

(click on image for better viewing)