Most likely you're running close to the capacity of your PSU. Anyway whats your specifications? It'll tell a lot.

Usually 12cm LED fans do not suck a lot of current during run time. It is the starting time where DC motor consumes a lot of starting current then it will stabilize. Try to do a reconnection. This time draw up a nice plan like fans and drives on one connection cable, graphics card on a dedicated cable, motherboard and CPU on another and so on.

If you're running to capacity of your PSU, usually you can detect this when some of your fans stops suddenly or a reboot in your pc. Some people might encounter random instability. These are some of the signs. If you're overclocking, try slowing down a little.