New build won’t start with MSI MAG A750GL PSU, any ideas?

robertgilbert86 · Saturday at 17:18

Hi all, I’ve just built the system below but it won’t turn on. When pressing the power button there’s sometimes a slight click, I think from the PSU, but then nothing.

When connecting my old PSU (NZXT Hale Power 90+ 550W) it will start up into the bios - I get a boot error but I imagine I just need to make it find the old SSD with windows on it. Didn’t have time today to work more on it.
One difference between the PSUs is the old one only has a 4-pin CPU power supply, whereas the new one only has an 8-pin - would that make a difference?
Annoyingly, Asus don’t seem to have an easily accessible key to read the motherboard lights, but they suggest no serious issues:

CPU - none
DRAM - none
VGA - solid white
Boot - solid green

Any ideas why it won't book? I’ve checked all the cables are seated properly and in the right sockets, and the power switches are working (as it starts up with the old PSU). Also done the pin trick on the new PSU and it will start up and read correct voltages from each pin.

Spec:

MSI MAG A750GL 750W 80 Plus Gold ATX 3.0 PCIE5 Modular Power Supply
AMD Ryzen 5 9600X Six Core 5.40GHz (Socket AM5)
Asus TUF Gaming B650-Plus WIFI (Socket AM5) DDR5 ATX
Corsair Vengeance EXPO/XMP (2X16GB) DDR5 PC5-48000C36 6000MHz
Radeon RX 7600 8GB
Crucial P310 2TB M.2 2280 PCI-e 4.0 NVMe Solid State Drive

pastymuncher · Saturday at 18:51

You are using the new psu's cables and not the ones from the old psu? Only ever use the cables a psu came with or you can end up with a expensive paperweight. If you are using the correct cables you haven't mistakenly used a 8 pin pci-e in the motherboard 8 pin socket? Pci-e will be 6+2 pins while EPS will be 4+4 pins. By rights they shouldn't fit but some do because of sloppy design. A 8 pin connector is preferred to a 4 pin connector so no that won't be causing this. You don't need to worry about the 4 pin socket as the extra power is only needed for extreme overclocking with the highest end cpu's. Just the 8 pin is more than enough for your 9600x and even my 7800x3d.

There is a chance that the motherboard is on a old bios that needs updating before it will boot with the 9600x. Your board has USB flashback so it isn't a problem. You need bios version 2613 or newer to run a 9600x, the latest is 3281. There is no reason to do incremental updates and you can go straight to version 3281 which you can download here. Rename it as per the instructions and put it on a fat32 formatted usb stick. I haven't used usb flashback for a long time so this next bit may not be correct and you should double check the manual to bee sure. You don't need to boot the pc, it only has to have power to it so power on at the wall, flick the switch on the psu if it has one and plug the usb stick into the correct port on the motherboards I/O panel (it's the second one down in the row of 4 usb ports and hold the usb flashback button (between the speaker sockets and the wi-fi aerial ports) down until the light starts flashing (around 3 seconds). Let it do it's thing (the light stops flashing when it's done) and do not interrupt the power. Hopefully you should be able to boot then.

robertgilbert86 · Sunday at 10:03

Cheers for the tips. The old PSU wasn't modular so it was all new cables in use, and this PSU has the same cables for PCIe and CPU so no issues there.

I've put my old PSU in now and it starts up and is running fine so I'm pretty sure it's only the new PSU at fault - the GPU and CPU appear to be working fine without a bios update.

pastymuncher · Sunday at 10:12

It uses the same socket on the psu end but the component ends are wired differently and "should" have different shaped "blocks" on the connectors but like I said, sometimes the cables will plug in where they shouldn't and can cause a similar fault to what you are experiencing so it's worth double checking.

DD_Crash · Sunday at 14:35

You could always buy a PSU tester to check its working.