That you can detect tgat it is turning off and on means that the battery is good .
The two most likely probabilities is that it is stuck in a corrupted startup, or the backlight has died. If the backlight, a tech can replace the display panel.
The startup routine is stored in executable form in nonvolatile RAM. The factory image is store in nonexecutable form in protected memory.
If it's a Startup problem, you can try to recover the tablet by doing a factory reset . This will recopy the factory image to nonvolatile RAM and make that copy executable. Your personal data not on an external sd card or cloud storage will be lost.
Turn it off, wait 30 seconds and then when you turn it back on, hold down the power button for one minute.
If you are lucky, the original factory image will be restored. The first startup will take longer than normal. Wait. This initialization procedure normally happens at the factory before shipping the tablets to customers, so it will not look familiar.
You may see either a DOS-like display with a few lines of text and/or an Android robot with an open chest panel as it initializes everything, and then the tablet rebooting by itself.
When this finishes, you can then reenter your wifi password, your gmail account info and reload your apps from the Playstore, My Apps, All Apps. Whatever you replicated to cloud storage should still be there.