Yeah you have got a decent setup with a bad PSU. RM is not up to mark. I think that one is the culprit, try another decent PSU (AX, HX, TX from Corsair, XFX, Seasonic) just to test, if it solves the problem then you are in business, else it could be your GPU.
What would happen if your PSU can't cope with the load:
•bad 3D performance
•spontaneous reset or imminent shutdown of the PC
•freezing during gameplay
•PSU overload can cause it to break down