Welcome to the forum!
There are a few options to look into here. It could be your backlight or display went out on you. What happens when you plug the USB cable (charging cable without the wall wart) into a computer? Does the computer recognize new hardware? What about after you hold the power button for 5 seconds and wait a few minutes?
If you have a microHDMI to HDMI cable, try plugging it into a TV to see if that works.
Does the wall wart work to charge other devices? Try it with a cell phone, or other USB device to see if it powers on or charges. If it does not, throw your wall wart in a plastic bag and put it in the freezer for about 10-15 minutes. Then remove it and wait another 10-15 before plugging it in to let it warm up a bit. (yes, sound wonky, but it works!)