If you're not doing any overclocking it should be fine using one 4 pin, but you should get in the habit of putting everything together properly, haha. Anyway if PSU spins hopefully that means it's working, if you had a multimeter you could test if further. If it's still not posting as of today, try stripping back to just a CPU, MOBO and one stick of ram. See if you can get a post. (Assuming you inbuilt graphics)