Hi,
Have you tried pressing the "reset" button on the back of the device?
Press to reset the tablet (then press and hold the Power button for 4~5 seconds to turn on the unit).
Try this and see if it resolves the problem in case it is a software glitch that is the cause and not a hardware problem
Also try the torch test.
Shine a torch at an angle close to the screen to check if you can detect a display at all. It will be very faint.
If you can there is a backlight problem with the screen, which will have to be further diagnosed as to the cause, faulty systemboard, faulty or loose video cable, faulty screen.
If you can't then again the problem will have to be further diagnosed as to the cause, except you know a bit more, i.e. not only is the backlight not working, the video is not working as well.