Have you tried to another gpu?
Can occur due lack of power on the power riser, try to change with different power riser like 6 pin/4 pin /sata or can be happened because of pciex1 or a cable on riser is broken.
Thank you. I already tried with another riser and another different power riser. This gpu still not detect.
So i very confuse went i use this gpu with x16 on board (not use riser card) the vga is narmal.Also i try with another computer with x16 on board the vga is narmal.
can you try to PCIex16 Riser?. I doubt a GPU only want PCIex16. but no problem if you want to try that. like this: