QUOTE(Skylinestar @ Nov 16 2020, 08:06 PM)
flex cable problem?

Not sure, but 1070ti on that same PCI-E riser, no issue at all.
Test swap few times, 3080 have issue, 1070ti no issue
QUOTE(Fizzy-Fiz @ Nov 16 2020, 08:08 PM)
its a pcie issue. is your board am4?
basically pcie 4 slot > pcie 3 riser > pcie 4 card
you can try to change in bios to pcie 3 but that might not work
QUOTE(Bonchi @ Nov 16 2020, 09:12 PM)
cough* riser incompatible with pcie 4.0 *cough (if your mobo is also pcie 4.0
I did suspect this, and configured all PCI-E 16 main slot to gen 3 in BIOS ( MSI B550 tomahawk )
No luck
I would guess if PCI-E gen version issue, either it boot or dont boot at all ?
What's weird is, 3080 on riser, can boot to win10 without issue, normal usage ( Chrome/youtube/install s/w ) all no issue. Just graphic driver 'appeared' missing, so Win10 fall back to it's own generic display driver.
QUOTE(sai86 @ Nov 16 2020, 09:41 PM)
as others said, you need to have pcie 4.0 riser instead. else via this method. plug in pcie 3.0 graphic card, boot into bios -> configure pcie lane to pcie 4.0 (depends on your mobo). turn off pc, slot in pcie 4.0 GPU. boot up.
else, get compatible pcie 4.0 riser.
https://www.youtube.com/watch?v=zxvCZWDR_bYI think worthy to try, tomorrow after work will try