Why does the RX460 graphics card not work in the PCI-e x16 3:0 slot?

Question

Video cards

Good day!
Motherboard gigabyte h61m-s1 ver 2.2
Processor intel core i3 2100
bought a MSI RX460 4GB OC video card, I plug it into the PCI Express x16 3: 0 slot, when the computer starts, the BIOS emits 1 long three short ones (the video card is not recognized), took the riser, connected it to pci-e x1 slot, the video card is up and running. For the test, I took another video card to check the pci express 16 connector, connected the gtx550ti, the system started up without problems, the drivers were installed, it works stably. What could be the problem? Why does the video card in the x16 slot not work, but does it work in x1?

Answer 1

No, seriously, only lamers read manuals?

*The PCI Express x16 slots support up to PCI Express 2.0 standard when an Intel 32nm (Sandy Bridge) CPU is installed.