B450M Steel Legend Not Posting after Radeon Update

I installed a new B450M Steel Legend with a new 3900X about 2 months ago. I also upgraded to 32GB of new memory. The power supply & video card (Radeon RX 580) were about 2 years old. I had a few troubles getting it working at the start (loose memory kept it from posting) but once I got past that it was working mostly fine until today.

Last week I had a BSoD but since it was just one BSoD I didn't investigate the cause. Then today the computer had been on for an hour or less. I was sitting next to it but it had been idle for a few minutes. Unexpectedly the screen turned green. I moved my mouse and the desktop came back. I thought maybe the monitor was going to sleep early but turned green instead of turning off. But just in case I checked to see if there were any video driver updates and there were. I downloaded the update and installed it. At the end of the process it prompted me to restart the computer so I did. Windows shut down and the computer restarted, but wouldn't boot or post.

Normally when powering it on I'd press the power button, there would be a 3-4 second pause before anything happened, then the fans would spin on high for a couple seconds, then they'd spool down to idle, and finally the motherboard would post and Windows would start loading. But after upgrading the video drivers the fans would spin on high and stay there. The monitor shows 'no signal'.

When I initially had problems with the loose memory the behavior was different. I'd click the power, there'd be a pause, the fans would spool up to high, then the fans would come to a stop and there would be a pause before the process would start over and go into a loop. Now the fans spool on high and stay there and I need to hold the power button down for 5-10 seconds for it to power off.

I've tried:
- Unplugging the PC, holding the power button down for 20 seconds to clear the capacitors, then plugging it in again
- Using each of the two HDMI ports
- Using a display port cable
- Resetting the CMOS

I DON'T know what the BIOS level is, but I'm pretty sure I updated it shortly after I did the upgrade 2 months ago.

Has anyone experienced anything like this£ Any suggestions on what might be amiss or how I could get things working again£ Is it worth trying to create a Windows install USB drive on another PC, or is it not even getting to that part£ Or is there another way to get things running in some kind of safe mode£

Any info or ideas appreciated!

ThreeDee wrote: do you have another video card ..anything .. that you could throw in your box for testing purposes£ Have you tried reseating the video card£ When you say "loose" memory .. do you mean you just didn't have it seated properly£ Maybe reseat everything ..CPU, GPU, Memory What power supply are you using (make/model)£ Have your tried installing your video card in the lower PCIe slot for testing purposes£ is the fan spinning on your video card£

I think I'm going to try to contact one of those computer repair services, not because I don't think I could figure it out eventually, but because I know I'll obsess over it until I fix it, and that would distract me from work and other things and would probably have me throwing money at parts that might not be needed. But I'll answer your questions anyway because I appreciate that you took the time to offer some help!

1. No, no other video card laying around sadly.

2. No, have not tried to reseat the video card yet. If I can't find a repair service to look it over this was the next thing I'd try.

3. Yes, sorry about that. The memory wasn't loose per say but it wasn't seated correctly. Once it was that problem cleared.

4. This would be my next thing to try after (2)

5. Power supply is a Corsair CX750M

6. I don't think my case is big enough to try using the lower PCIe slot.

7. Yup, the video card fans are spinnin'!

A little late here but after verifying everything is seated correctly I'd say it would be worth reflashing your ROM chip as theres a few things in your descriptions that suggest there might be some corruption setting in. As you mention your GPU is a couple years old I'd also take it apart to give it a thorough clean and some new thermal paste and pads to ensure nothing is overheating a green screen in my experience is usually linked to the vRAM being unstable, either through heat or bad memory timings. Have you tried applying modified memory timings to your RX580 with anything like Polaris BIOS Editor?