You PC has that issue. A GTX-1080ti will not boot in your PC because it has a legavcy BIOS.
The GTX 10820ti only hs support for a UEFI BIOS.
You will need a graphics card that supports either legacy BIOS or supports UEFI\legacy BIOS.
Sapphire tech makes powerful video cards that will work. They will have to be AMD Radeon R9 or R7 cards.
Take a look at the R9 300 series cards. They have the power you seek with up to 8GB of discrete memory.
http://www.sapphiretech.com/productdetial.asp?pid=F107EA58-6C33-4F74-A739-03FF852D34A1&lang=eng

I am not an HP Employee.
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For laptops or desktop PCs, use the Fn+Esc keystroke while logged into Windows to locate the Product number (SKU)