New PC, not turning on when power button is press... but RAM lights tu

I suggest that you remove the MB and do a barebones set-up on a piece of cardboard (make sure it is larger than the MB) only connect the PSU, the GFX card, screen, 1 stick of Ram and the keyboard.

IF your MB doesn`t have a power  test switch you will then need to short out the 2 power on pins on the MB header to get the PSU to activate, you can use a small flat bladed screwdriver or a paper clip bent into a U shape, this is perfectly safe if you do not touch anything else, the idea is to see if we can get a BIOS screen if you do you can then add one component at a time until you find the problem component, you must power down and remove the power cord from the wall before adding another component, second suggestion try a known working PSU, it is not unknown for new components to be bad.

 

Any questions along the way let us know.