Did you enable Legacy in the BIOS under USB controller ???
Legacy allows 2.0 to work on 3.0.
The two next to the PS/2 should be 2.0, they are for keyboard/mouse with USB.
If your case has USB 2.0, then you need to plug into the header # 20 or 21, as these are 2.0.
The header on the mobo for USB 3.0 is # 7, it's the only one towards the front of the board- near drives.