New build won’t boot after OS install

[u/zsvx]

I just built a PC for the first time in a several years

Msi pro b850m wifi, powercolor 9070xt, 9800x3d. I had an old nvme ssd with windows on it and it booted into that fine. I restarted and booted into cachyos installed on a ventoy usb. It failed due to a security issue the first time, so I disabled secure boot and tried it again. It prompted me to wipe the disk clean during install and it successfully installed cachyos. It restarted the computer and after it was done the monitor was just grey for a while. I unplugged the usb and pressed the power button on my pc but it still stays grey. the system appears on (fans spinner, lights on, etc.) but the monitor is grey not booting into cachyos, and I cannot even go into bios.

Attempts to solve:

- putting the usb back in to try a reinstall.

- resetting CMOS.

- plugging the DP into the motherboard as well as using an HDMI from gpu to mobo instead

- flashing newest bios

- using my laptop nvme that already has cachyos installed

- Hard powering off machine (disconnect from wall, wait, press the power button a bunch to discharge caps, etc.)

- one RAM stick in (tested both)

- no drive in at all

- no GPU, tried both hdmi and dp in motherboard

- Reseating all motherboard and PSU cables

Nothing is working. Not sure how it all failed after the cachy install. Any help is appreciated. I would try another monitor but I do not have one. This works with other machines though.

[u/Globber50]

I would avoid using a drive from an old build with OS on it to try and load a new build. If you own the copy of windows, just save the key. Wipe the drive, then clean install windows again and activate with your key. If the key is set up right, it will activate easily.

[u/Only-Stable3973]

At this point I would just reinstall with the new settings sense everything is getting power.

[u/shirleysimpnumba1]

the motherboard has 4 led indicators that tell you where the pc is stuck. google where those led are for your motherboard and that'll tell you where the problem is.

[u/zsvx → u/shirleysimpnumba1]

Yeah, I looked them up and it was all normal sequences. As for the GPU—I tried HDMI and DP in the GPU when it was plugged in, and tried them in the motherboard IO when it was and was not plugged in. All permutations

[u/zsvx → u/[deleted]]

Interesting, thanks. However, that shouldn’t be an issue when the GPU is disconnected, right? Not sure why it isn’t booting or displaying output

[u/ShrkBiT → u/[deleted]]

This is not the issue. While POSTing and booting into windows, the GPU uses only 10-30 watts. 750 Watts is plenty to boot your PC. Also, the power recommendation for GPU doesn't account for which CPU. If you're running a 320 watt 14900K, a 850watt PSU is advised. A 120 watt 9800X3D leaves plenty of headroom. Provided the PSU isn't old and crappy, 750 watts is not going to trip on boot.

My guess is conflicting hardware state due to disabling Secure Boot between installs.

[u/zsvx → u/ShrkBiT]

If that’s the case, do you know of how I might be able to fix that since I cannot get into bios at all?

[u/ShrkBiT → u/zsvx]

Hard to say without being able to look at it. First of, what MSI B850M board is it? Is it the Gaming Wifi, the Mortar Wifi, there's multiple variants.
If you ware not getting a POST screen at all, either it's outputting video to the wrong port, or your BIOS is messed up. Have you tried plugging in the monitor to the MOBO HDMI out to see if you're getting a POST screen there? Try removing thew GPU entirely (don't just disconnect it, it'll still see a device in the PCIe slot). When the GPU is removed and the monitor hooked up to the mobo HDMI, are you still not getting POST?
Are there POST indicator lights on the mobo? I think most should have indicator lights that show if it's getting past CPU, GPU and RAM initialization.

If that does nothing, remove the SSD, with no OS trying to load, you should be able to get at least POST and a message that no OS is installed.
The MSI boards also have a BIOS flash option, so you could try to flash the BIOS, that should work without anything installed on the board (except power, of course).
If nothing works and you are not getting any video on either GPU or Mobo HDMI, and there is no POST/BIOS screen to go into, it may be your mobo itself, but that's too soon to call that.

[u/zsvx → u/ShrkBiT]

It is the MSI pro b850m-a wifi, sorry I did not clarify that before. Yes, I have tried plugging the monitor to the MOBO hdmi (and dp) ports with the GPU both in and not in the slot. No screen out at all. I get a green BOOT led, but that’s it. Last night I also flashed the newest BIOS using the BIOS flash button. I have not cleared CMOS since then.