Windows sound muted?

Hi, I just bought Cubase Elements 8 today, so I am a noob.

I faced this problem from the start, whenever I open cubase I can’t hear anything inside of Cubase.
This is solved by going to Devices -> Instruments, and selecting whatever I think is good, I do this until I hear something from Cubase. So whenever I solved that issue, I want to go to the internet browser for tutorials, so I can learn with my browser and Cubase open at the same time. So whenever I do that, I can’t hear anything from windows, absolutely nothing. HOW DO I FIX THIS?!

Thanks a lot!