Most likely it's a loose wire or bad relay on the power distribution board, (bus?), I would re-seat every connector first (WITH THE SYSTEM OFF!). I've seen computer CPU's, drive connectors and memory unseat with a 50 degree F. temp change (warm house to cold car and back).
If the laser is coming on, it shows you have power for that line/voltage, the laser more than likely runs at a different voltage from everything else, make sure all necessary voltages are being supplied. Even if you have them all, it doesn't necessarily mean you have enough amps, the laser can fire with lower amps/watts than spec, see if it's firing with any power by seeing it it can punch through something. That looks a cheap Chinese PSU, they are often under specc'd by 10-25% or more and if you pushed it, it may be supplying even less now.
It's confusing when you say "stepper", too many things are termed stepper, are you referring to the driver, the motor or the controller itself? You say the stepper has voltage, but what are you referring to? Also, not sure if it matters, but in the first pic, you have one led lit, and two in the second on the controller.
By the way, you said this was a temporary setup, one thing we were warned with on ours was that the laser itself could cause RF(?) interference with the controller or stepper drivers if it was too close to them without shielding, causing all sorts of oddities. I'm guessing yours has a bit less power, but the warning still stands.
