Why cant my cpu type a letter and move cursor at same time?

-im trying to play an online game where you need to move around using the keyboard and move the cursor to aim, but my cursor stops moving if i press a letterare you using a passive hub to connect the keyboard and the mouse to the computer via one usb port?

if so , remove the hub and find another solution (a wirelss keyboard and a mouse with an infrared usb receiver)