spoiler
I very limited as to what computer hardware I have access to in where I live (not the USA), but I managed to get my hands on a used HP Elitedesk 800 G3 SFF and waited months for an AMD FX 6400 Low Profile to arrive. Now I am having trouble with this card.
I know the reviews state that the card can't take advantage of my x16 slot bandwidth, but I expected to be able to use it in that slot, as the x4 slot is right against the power supply, and the card doesn't breathe well at all there, and thermal throttles.
However, when I slot the GPU in the x16 slot, the PC won't POST. I find no settings in the fairly limited BIOS options that would prevent this, and a test Nvidia GT 720 works in the x16 slot just fine.
I'm out of ideas to get this to work. Legacy/UEFI Option ROM settings make none. The port is enabled in the section that toggles availability.
I thought this would be related to my M.2, but the 720 is a x16 lane card, and it works fine in the x16 slot, so now I'm just left scratching my head.
Anyone have experience with this issue? Most results I find on my search terms are for custom builds with more BIOS settings than a business-class HP Elitedesk. That said, my search-fu is not what it once was before my mental illness advanced, and now I can't as easily assimilate information, so it's possible I am missing something right in front of my face.
EDIT: After days of fiddling, I made this post and went back to troubleshooting. It just booted with no problems. Scratching my head, but something I did in passing was the trick. Now to make sure I save these exact settings!
EDIT2: It turns out it was always working, and it is just BIOS/UEFI screens that will not display. This kept me from installing my base OS at all until I moved the GPU to the x4 slot. Since I installed the OS with the GPU in the x4 slot, now it boots to the point where I enter my luks encryption key and I'm good, but it still won't show the BIOS screens. Perhaps I need to enable the legacy Option ROM for video?
I hate to even ask, but you are plugging your video cable into the video card and not the onboard integrated graphics I hope?
Strip it down to a minimum. If it's got two sticks of ram, make it one. Unplug all drives, remove nvme if it's on the board. Unplug everything but a simple USB keyboard.
Check it boots. Yeah? Pop your GPU in. Does it boot? No?
Do you get fan spin? Does the board have an indicator light, or is it like a dell where failure to post will (hopefully) blink the power light in a coffee sequence? Does it just power right back off?
What wattage is the PSU, and how much extra load does this dgpu put on it?
If it DOES boot with minimal hardware plus the GPU, put one thing back at a time till you find the culprit.
I'd also suggest logging into a live os of some sort, and running lspci -vv and seeing if the card shows up correctly, be it in the x4 or x16 slot. Id also suggest trying any other x16 pcie card you've got lying around, and checking it functions.
If the GPU has two (or more)outputs, did you try each?
Oh and check the bios for options related to default GPU. Dells definitely have this option.