B450M Pro4 x16 PCI-e issue

I am building my new system with following specs:

Ryzen 5 2600x with OEM cooler (no overclock)
B450M Pro 4 (board came with BIOS 3.8, site says not to use 3.9 with Pinnacle Ridge (but so does 3.6, and I don't see 3.8 listed).
G.Skill Ripjaws V DDR4 3200 32 gig
WD Blue 550 NVMe
Corsair CX 650

I am having issues with the x16 PCIE slot and an old 9800GT (a placeholder card while awaiting my GTX 1060).

The system will not even post with the 9800GT in the top x16 slot.
Just powers on, CPU and GPU fans spin up high speed, and then the CPU fan ramps down, then back up, and keeps doing it till I turn it off.
The card works just fine if I use the bottom x4 slot.
The card also works just fine in other systems (even another B450 build, using a Gigabyte board). Have used 2 seperate PSU's, so I know it is not the card or power supply.
Used 1 stick of RAM, different brand of RAM, all with no changes. RAM tried at standard and XMP settings.

I have a HD5450 that does work just fine in the x16 slot.

Is the 9800 GT just too old to work with this board?
I adjusted some of the PCIe setting in the bios (Auto/Gen 1, Gen 2, Gen 3, changing the card to 2x8 vs 1x16), but there was no change.

I just want to make sure it is not a board issue with Nvidia cards since I have a 1060 on the way.

still having this on going issue with a friends system
AND his 1060...................
originaly i cured it by changing the pcie gen from auto to gen3

but when he fitted it to the case it reverted back to not displaying/booting with the 1060 in the pcie x16

the system is located too far from my home to physically test and find a cure myself ,so waiting for him to have time and inclination to test anything else with me over a phone call
i will link him to this post as it may help thanks

yes ive found out he is using a convertor to run a second very old monitor

it does work on the x4 slot like that but not in the x16