Question Help! Ryzen 9 3900XT not posting!

[Inventor_T]

Hi,
I’m trying to complete my build with the Ryzen 9 3900XT but ran into a weird problem.
So when I tried to post; the debug light on the motherboard stays on VGA. Originally I thought it was the graphics card (PNY xlr8 rtx 2080 super) and ran all the normal diagnostics but graphics card works fine (installed and tested in another build).
Eventually after trying a new motherboard, graphics card, running all the normal diagnostics (swapping out ram, clearing cmos, updating bios etc); I swapped the Ryzen 9 for an old Athlon CPU and it worked perfectly.
CPU isn’t faulty; the pins are clean with no broken or bent ones. Can’t figure out a solution. Someone please help. My system specs:

Motherboard: ROG strix B550-F
CPU: Ryzen 9 3900XT
RAM: Corsair vengeance RGB pro 16gb (8*2) 3600mhz Ryzen tuned
Cooler: Kraken z63 AIO
PSU: Corsair rm850
Name: Western digital 1tb
Graphics card: PNY Xlr8 GeForce RTX 2080 Super

 

[mdd1963]

the 3900XT is a more recent CPU, intro'd only a few months ago.

Did you update the BIOS to a version within the last couple of months (preferably the latest) that supports the 3900XT, vice merely the 3900X?

Disconnect all drives, and drop to one stick of RAM until you can get a POST....

 

[Inventor_T]

the 3900XT is a more recent CPU, intro'd only a few months ago.

Did you update the BIOS to a version within the last couple of months (preferably the latest) that supports the 3900XT, vice merely the 3900X?

Disconnect all drives, and drop to one stick of RAM until you can get a POST....

Updated the BIOS and tried to post again; no luck.