midi signal but no vst sound


I have Cubase artist 8.5 installed in my PC and I recently added UR22 mk II. I use a keyboard to play/record midi notes into Cubase. However although Cubase registers the midi note in the transport panel, no sound is heard. On the track I have tried using various Instruments to no avail. I can play the instrument with the mouse and it will sound. I have also used Midi-Ox to check the incoming and outgoing midi notes and that shows the notes are being received. Can you please help.

I can use the midi keyboard via the UR22 mkII with my other recording programs without any problems.