Simple test:

Power up just the motherboard and it should give you an error that there is no cpu. Then put a cpu in it and it should give you an error that there is no ram. Then put ram in it and it should give you an error no gpu. Put a gpu in it and it should work. Now if:
  1. Motherboard did not produce an error in any of these steps it is broken.
  2. If the motherboard gives a cpu error when the cpu is in than it is bad
  3. If it gives ram error when ram is in the ram is bad
  4. If it gives gpu error when the gpu is in the gpu is bad
  5. If nothing occurs the psu is bad

You should run the psu on a psu tester which you should own b.c they are only like $10 and are important for figuring out where your problem is.