Not able to use all 3 PCIe slots on Intel Server board S3420GPLC with Xeon X3470

[AmazeQ]

I have Intel Server Board S3420GPLC with Xeon X3470. I have been using it for more than 6 years now. Mother board has 3 PCIe slots and all of them working individually or in any combination of 2 PCIe slots. But as soon as I populate 3 PCIe slots with graphics card, Device manager in windows stop recognizing any graphics card in the system. [Little note here, all graphics card is working here and I have run any combination of 2 graphics card together on system without any issue]

I am not able to figure out if there is any kind of bios setting which I need to change to so all 3 slots run at the same time.

If anyone has solution to resolve this issue, please help.

Resources:
https://ark.intel.com/content/www/us/en/ark/products/46533/intel-server-board-s3420gplc.html

https://ark.intel.com/content/www/us/en/ark/products/42932/intel-xeon-processor-x3470-8m-cache-2-93-ghz.html

[SergioS_Intel]

Hello AmazeQ,

Thank you for contacting Intel Customer Support.

The interactive technical support for the Intel® Server Board S3420GPLC you have requested has been discontinued. 

Due to this product being discontinued, Intel Customer Service no longer supports inquiries for it, but perhaps fellow community members have the knowledge to jump in and help. You may also find the Discontinued Products website https://www.intel.com/content/www/us/en/support/articles/000018497/server-products.html helpful to address your request.

Thank you for understanding.

Best regards,

Sergio S.

Intel Customer Support Technician

For firmware updates and troubleshooting tips, visit :https://intel.com/support/serverbios