Your motherboard supports PCIe 2.0 and your new card is PCIe 3.0, which claims backward compatibility but is not necessarily true. You can try changing to UEFI boot if not already. If you are not UEFI boot, you would have to reinstall the OS.
Now, you may find older PCIe 2.0 cards on the used market. BUT... The best thing for you to do is to get rid of that old board and get a new(er) board this is supported.