Power Supply wont power on when plugged into computer

[Justin_48]

I'm building my first computer but once i turned the power supply on, nothing was working. The fan on the psu wasn't even turning. So i unplugged everything and tested the psu separately and it turned on. If i quickly plug the 24pin into the motherboard after the psu was on, the fan on the cpu turns for a little bit but stops. Any help would be greatly appreciated. psu is a evga 430w and motherboard is gigabyte b85m-ds3h-a.
edit: with the power switch of the case plugged in the the psu and CPU fan power on but 5 seconds later turn off. then after off for a second, it turns on for another 5 seconds.

 

[turkey3_scratch]

You shouldn't be plugging the PSU into the motherboard while it's on, and most like your case switch cable is plugged in incorrectly.

 

[Justin_48]

i was testing it outside of the case, with nothing else plugged in.

 

[Justin_48]

You shouldn't be plugging the PSU into the motherboard while it's on, and most like your case switch cable is plugged in incorrectly.

i was testing it outside of the case, with nothing else plugged in.