A Clockstar that will not start after a build is nearly always a solder joint that has not quite taken rather than a faulty board, and it is usually fixable in a few minutes with the iron you already have.
Go over every pin and compare what you see against this:
A good joint is a small shiny cone, a little volcano shape, that covers the round pad completely and hugs the pin all the way round.
A poor joint is dull and blobby, or sits on the pin like a ball without touching the pad, or leaves bare metal showing.
A bridge is solder running across to the pad beside it. That has to come off before the board will work.
Solder must come through and cover the bottom of the pin, not only sit on the top surface of the board.
Reheat any joint you are unsure of, add a little fresh solder, and check that no stray solder is left loose on the board. Then power the Clockstar up again and see whether the display comes on.
If it still does not start, email us at [email protected] with photos of the front and back of the board, and we will go through it with you.