Black Screen - tried hard reset

If you've powered it off, you will likely not get a response from Siri until you unlock the device for the first time. The device is in a fully locked state, that's why it requires Pin/passcode rather than Touch ID if it has been powered off. I just tested this on my personal iPad and I get a "Unlock this device to use Siri" prompt if I try to invoke Siri before this initial unlock.

It sounds like yes, the backlight is okay, that's why it lights up and then fades out. Because it's responding to the power/home button, but you're not unlocking the device so it's timing out and then going back off. So it seems as though you're just not getting any image.

If you've already done force restarts and you get the charging sound when you plug in (which AFAIK only occurs if the device is powered on). I think it's safe to say you probably need a new display. I would check and see if the device is recognized by the computer when you plug in. You may need to open iTunes to be able to tell, especially if the computer is a PC.

Of course it's possible it's a more serious issue, but my first thought is definitely display.