Is the switch on the power supply flipped to the " I " position?
Check everything indicated at the following link, and I mean every little thing. Double check each connection even if you think you already have, especially the 4 or 8 pin CPU power plug and 24 pin mother board power plug as well as making sure the RAM is all FULLY seated.
I have a cosair cx 600m as a PSU. I have it connected to a gigabyte h81m-h MOBO. Any ideas on why it is not working?
The CX series PSU has poor 24 pin latches. Push the latch harder till you hear a click if you have not heard it previously, remember do not push it too hard!
I remember when I built my computer with a CX PSU, my PC won't start up, so I pressed in the 24 pin latch much harder and I finally heard a click. I didn't think my motherboard liked that though...