A screen that stays dark after a build is nearly always one solder joint that has not quite taken rather than a faulty board, so it is usually a short fix with the iron you already have. This applies to the original Jay-D kit rather than Jay-D 2.0.
Check every pin on the board, starting with the screen header. Make sure each pin is soldered, that no solder bridges two pads, and that there is no loose solder left anywhere on the board. The solder must come through and cover the bottom of the pin, not just sit on the top surface.
A good joint is a small shiny cone, a little volcano shape, that completely covers the round pad and hugs the pin all the way round. A poor one is dull and blobby, sits on top of the pin like a ball without touching the pad, leaves bare metal showing, or runs across to the pad next to it. The photo at the foot of this article shows both, with the sound ones marked OK.
Reflow anything that looks wrong, let the board cool, then switch on and try again.
If the screen is still dark, message us here, or email [email protected], with your order number and a close photo of the board, and we will help you sort it out.