Question PC refuses to POST when GPU is in PCIE 4.0 x16 slot, but works in a lower bandwidth slot ?

May 14, 2024
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I've encountered a rather weird problem.

So, I've finally received my new PC parts, I have first made a test bench the moment it all arrived. And when I inserted the GPU into the PCIE x16 slot, it didn't POST...

The motherboard showed me a white LED near the VGA label.

I almost thought the graphics card was dead but when I put the GPU into the lower x16 slot with way less bandwidth, for some mysterious reason the PC decided to POST successfully.

Checked GPU-Z, and it shows that the GPU is running in x4 mode, but supports x16 3.0 mode? What the heck?

I've tried changing the slot's mode to Gen3, assuming my GPU just couldn't work with Gen4 mode. But nope! It just didn't post again!

I'm not sure if it's a defective motherboard or just the GPU's fault, but it's all new parts except for the GPU and RAM!

Here's my specs:

MBD: MSI MPG B550 Gaming Plus
CPU: Ryzen 7 5700X
GPU: Asus Rog Strix RX 570 OC 8GB
RAM: 16GB DDR4 2400MHz
 
May 14, 2024
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Checked GPU-Z, and it shows that the GPU is running in x4 mode, but supports x16 3.0 mode? What the heck?
That just means - the card is x16 and it is placed into x4 slot.
Second x16 slot on motherboard electrically is only x4.
I've tried changing the slot's mode to Gen3, assuming my GPU just couldn't work with Gen4 mode. But nope! It just didn't post again!
Try forcing it into PCIE 2.0 mode.
Are you using any PCIE riser cables?
 
May 14, 2024
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bios updated? it's essential for compatibility
I've used the BIOS Flashback feature on my motherboard, apparently my BIOS version is from 2023. Now it's updated, July 2024.

I've plugged the gpu into the x16 4.0 slot and.. it didn't POST, again. The VGA debug LED is still turning on and there's no signal out.