PSU missing wire

[#1]

I was asked to fix a PC that had started to turn itself off intermittently. By the time I got my hands on it it would barely get past the POST before going off. I suspected PSU straight away and upon checking found that a white wire (pin 18 -5v) is completely missing between the PSU and the motherboard. Is this causing the problem? I'm not sure because i'd have thought if it was never present then the PC would never had worked at all.
Same PC had a bad fry couple of months ago and I replaced the motherboard and PSU and it's worked until now.

[#2]

Quote from: jmart

Same PC had a bad fry couple of months ago and I replaced the motherboard and PSU and it's worked until now.

Was the white cable missing then?
-5V is not used much on current PC, possible audio and RS232, but nothing else uses negative voltages. Hence why the PSU manufacture can omit it.
Chilly

[#3]

I assume it was. No one else goes into the machine and there's no evidence the wire ever existed. The board does have onboard audio and that's worked fine as well.
I'm just going to take out my PSU and hope it works with that. Since the last problem though, it's been plugged into a surge proof extension and according to it's sticker the PSU is only 10 months old.

[#4]

If it has been working fine since you replaced the PSU then that voltage rail is not required.
But, not having the wire does mean the PSU does not meet the necessary standards for ATX PSU's. Even if the voltage is not used on that Mobo, it is still a standard voltage that should be supplied by the PSU. If they have broken that standard, what else have they done internally? This may just has been a cost cutting exorcise though as -5V is rarely used now.