ok recently i changed motherboards but that didn't wen't quite well so today i'm changing it back and i messed up a little, my sys_fan is 3 pin and there is only 1 plug left but it seems not to fit correctly here are photos of it:
by the way , when i put this plug in sys_fan and try to turn pc on the only thing what happens is power button led quickly blinks and then nothing happens , but when i take it out from sys_fan all fans starts to spin but very slowly
Definitely a floppy drive power connection. Also could have been used to power an older style graphics card. Unless you have a floppy disk drive in your system, it shouldn't be connected to anything.
As said its a floppy power connector.
Great way to fry your motherboard by plugging that into your sys_fan! Don't do it! Your feeding power into your motherboard the wrong way!