Take a look at this link. It recommends that you download and try the free asio4all driver.
BTW… I too have a Realtek audio card that came with my PC (not on the motherboard). I never could get it to work correctly with Cubase do to very high audio latency. If yours does not work, search to find/purchase a ASIO capable USB audio interface. They cost about $100 (even less, I’ve seen them on sale for $49-$79).
Good luck. 
Regards 