So I’m having a problem with my pc, I just upgraded it to a a520-m pro motherboard, it’s got 32gbs of ram, it’s got a ryzen 5 5500 cpu, a msi 850w psu, and a msi rtx 3070ti and all these parts are brand new it’s even got all new cables and everything well I’m having a issue where it won’t turn on, I can verify it’s getting power because once I hit the power button and if I have my mouse or keyboard plugged in it turns it on but here’s the weird part, it has power to the usb ports and hdmi and everything as long as the power button is being pressed, but the moment I take it off everything shuts off, but no fans will turn on, no displays will turn on, and no rgb will turn on and im very lost because i verified it and everything should work great together but for some reason its doing this any ideas?
What is the exact motherboard you have? This really sounds like a BIOS compatibility issue with the Ryzen 5 5500. Some of A520 boards don’t support that CPU out of the box, and when that happens you’ll get standby power (USB lighting up) but the system won’t actually stay on—exactly what you’re describing. I’d check the CPU support list for your exact motherboard and see what BIOS version is required. Also worth double-checking that the 8-pin CPU power cable is plugged in (and that it’s the CPU/EPS cable, not a PCIe cable), because missing that can cause the same symptoms. there are a few other less common issues that could be but try Them first.
Did you mix and mach psu cables? If yoy did than use only the cables that come with the psu. But do what @Viraco said and check the motherboards compatibility.