I plugged in my pi to my hdmi screen and I've been getting a screen with just lines on it going up to down. It makes sense as this hdmi screen does not have a video scaler so unless you get the resolution right there could be some issues... The guide to the screen which can be found here: https://learn.adafruit.com/adafruit-5-800x480-tft-hdmi-monitor-touchscreen-backpack/raspberry-pi-config says to use the config.txt file to change the settings around... I can't seem to find a boot folder on my sd card. Here is a picture of the contents:
I believe that is an unused NOOBS card, as it is identical to what's shown here.
Of course, this puts you in a bit of a circular bind, because to install an actual OS so you can adjust
config.txt you need the display to work. I realize NOOBS may come with Raspbian pre-installed but I'm guessing you still have to go through the initial OS selection procedure.
Another answer there mentions a
noob.config file although you do not appear to have one. You might consider poking into that
os folder, but I would first try plugging it in, and hitting 2 if the display is blank.