pin 20 is the -5v, pins 17, 18, and 19 are common. that's why missing 18, you are still ok.
First time poster as until now I have been pretty competent on fault finding and research to rectify problems, but this one has me stumped.
I have recently upgraded my Thermaltake 400w PSU to a Thermaltake 600w W0355 PSU. I have noticed that on the 20+4 pin connector that the white wire (-5v connector?) is absent from the new PSU. Pin 18? I have read that this is not a necessary connnector, however, without it I cannot power up my system. The previous 400w PSU had this wire/pin.
I have an ASUS Striker Extreme MOBO. All the ancillary indicator lights come on when connected (USB, Fans etc) but the power button is non-responsive and the power switch lights on the MOBO do not illuminate.
If anyone can provide assistance it would be greatly appreciated.