Mystery solved! I managed to get a hold of some known good parts: psu, gpu, and ram. I figured I had a dead cpu but to my surprise it booted into the uefi screen, so I swapped my own parts back in one by one until it stopped booting. Turns out the Corsair Vengeance sticks are causing the problem.
Lesson learned - next time I will definitely start with a breadboarded bare minimum set up and add on from there so I don't end up with surprises trying to power up a fully loaded case.