Cubase 8 Stereo Mastering "Can't hear nothing"

So I start a new project opening up “Stereo Mastering” I drop a Song I want to master, on to the “Mixdown section”

I press play? can’t hear nothing, I Checked all my VST Connections, Resetted them multiple times, still doesn’t work I can’t hear anything I’m Wearing Beats Headphones Solo’s, Iv tried Plugin in my Speakers had It work 1 time, now doesn’t work at all. Someone please help me I don’t know if I might have accidentily hit some buttons I don’t know please help me.