No power to Motherboards from PSU

StellaMan · 27 Nov 2025 at 14:44

I hope someone can help me … I have replaced a gigabyte A520M H motherboard and a Corsair CX650 PSU with an A520M S2H and a CX750, but when I turn the PC on nothing happens, nothing at all. If I plug the PSU into a tester, all lights come on. I have tried shorting the power switch with a screwdriver between the 2 pins, but again nothing happens. As an experiment I plugged the old PSU into the tester and all the lights come on, plus the PSU fan spins, however, if I then plug the 24 pin plug into the old motherboard and turn it on, the PSU fan doesn’t spin. If I use the new PSU with the old motherboard, the exact same thing happens, so I’m wondering if there is a connection although I don’t know what on earth that connection could be ‍

!!!

Glanza · 27 Nov 2025 at 16:36

Did you forget to connect the 4 / 8 pin cpu power cable?

MissChief · 27 Nov 2025 at 16:39

Connected the front panel connectors correctly?

StellaMan · 27 Nov 2025 at 17:59

Glanza said:
Did you forget to connect the 4 / 8 pin cpu power cable?

No

StellaMan · 27 Nov 2025 at 18:00

MissChief said:
Connected the front panel connectors correctly?

Yes, double and treble checked that …

Blackwhite · 21 Dec 2025 at 02:09

Looks like there is problem with your motherboard

darkblade · 21 Dec 2025 at 15:09

So to be clear - you not able to use the old motherboard, old PSU and the old power cables? Those were previously working before you changed anything? (I think that there are differences on newer Corsair cables compared to older ones)

skankmaster · 7 Feb 2026 at 06:10

I had an issue showing similar results between swapping out a seasonic for an msi psu. Mixed the pcie with the cpu cable during a late night upgrade. Also I'm sure when examining some of the cables the shape of the cable pin sockets looked different between the two brands which added to the confusion. Oh the joys of incremental upgrades every 5 years.