Hello,
Please go to your Control Panel, Programs and Features, Uninstall a Program, and uninstall the Yamaha USB Audio Driver from your PC, restart your PC, and then install the latest driver version below:
http://download.steinberg.net/downloads_hardware/Yamaha_Steinberg_USB_Driver/PC/1.8.3/YSUSB_V183_Win64.zip
Please double-click on the downloaded ZIP-file. Another double-click on the “Setup.exe” file will start the installation.
Next, restart your PC again, and then download and install the latest Cubase AI 7.0.7 update below:
http://download.steinberg.net/downloads_software/Cubase_LE_AI_Elements_7/7.0.7/PC/Cubase_LE_AI_Elements_7.0.7_Update_win.exe
Then, open Cubase and go to Devices, Device Setup, VST Audio System, and see if the Yamaha USB Audio Driver shows up as being selectable, and reply to this email and let me know the result.
Hope this helps!