VST Plugins Not Hearing Sounds


I have a Mac Book Pro and Using Cubase AI, I am not able to hear any of my plugins sound software, I have been using both Motif XF6 and M-Audio Mobile Pre USB as sound drivers, any suggestions for solutions?

Do you have reference monitors (speakers) connected to the Left and Right line outputs on your M-Audio Mobile Pre?

What specific operating system and version are you running on your computer?

Thank you.