VST instrument no sounds

When i add vst instrument (Seven Slate Drums plugin) I hear no sounds. I did not have this issue before. What may be the cause? The bar goes up meaning the sounds are working but i cannot hear them through my headphones. I attached an iRig Keys I/O and i can hear the keys but not the vst plugin.

I have my irig keys i/o connected and now i only hear vst instruments but not the midi input (keys). completely opposite now.