PC won't boot if SATA power cable is plugged in

[Pointless2Play]

So I recently bought myself all new parts. I finished building my PC, but I waited with connecting the fans as the cables were getting in the way. After the PC started and everything worked as intented I went to work on the case fans. As I'm new to building PC's I knew all about the parts but not about RGB. I found this SATA cable connected to the chip in the back of the case. I plugged it into my Power Supply whilst the PC was on for some reason (pretty stupid I know) and the leds in the fans immediatly went on but were freaking out a bit so I decided to restart the PC. The PC wouldn't turn on. After removing this cable the PC did turn on again and I can still plug the SATA in when it is on and the leds in the fans will go on but if the PC is off and I plug it in it doesn't work.
Case:
Sharkoon Nightshark RGB
PSU:
Corsiar CX750

Thanks,

P2P

[FrostyRob]

Not exactly sure what "chip in the back of the case" you're talking about.  If you plug a SATA cable from your PSU into a SATA powered item (such as a fan or a drive) it should not damage anything even if the power supply is on.  Now if you plugged in a completely new set of cabling into your power supply as in a new piece of the modular cables I am not sure if this could damage your PSU or what it is powering or not.  It sounds to me like you have a short somewhere.  And what do you mean the LEDs in the fans went on but were "Freaking out a bit"?  A little more info may help us diagnose your problem