VST Amp Rack

Hello, I am such a CUBASE newbie so I hope my question makes sense to you folks.

I was just messing around with C7, just got it, and wanted to record something silly just to see how things work. I created a drum track with Groove Agent One and some guitar tracks. I inserted the VST Amp Rack and went to town. I took a break and came back to my project and started everything up again and now I don’t hear the VST Amp Rack when I play… I just get a clean sound. When I try to use the tuner on the amp rack I see that I get no signal.

This all started when I changed the buffer size (I use a UR28M audio interface).

Did you try restarting Cubase?