Question 3090 not working in 4.0 x16 slot but works in pci x8 slot -- why?

[Antmenpclove]

3090 in pcie 4.0 x16 slot doesn't post ez debug light is on card is pushed in locked no post

but 3090 works in 3.0 x8 slot why not working in first slot 3950x has 24 lanes I have a m.2 could that be the reason why its taking me slot or no?

 

[rgd1101]

full system spec? include make and model of the psu

 

[Antmenpclove]

full system spec? include make and model of the psu

Ryzen 9 3950x 16 core
MSI x570 gaming pro carbon
128gb ram 3200mhz
RTX 3090 ftw3 ultra
1000w psu windows 10 pro 2 m.2 I remove them and everything 3090 works 4.0 8x in first slot and second with changes to bios if I try to put 4.0 x16 the VGA light comes on and card doesn’t post if I go to bios and out pcie 8x8x or 4x4x4x4 the card works and some times it just gets stock loading I have to reboot… is my motherboard or 3950x doesn’t support 3090 I change psu for more power same problem do I need a new cpu and mobo or just mobo