Printer app won't force quit on macbook air - not showing up in activity monitor either

I used a HP printer to print something out and for about a week, the application for the printer (titled HP ENVY 7640 series) has said it is not responding. I tried force quitting, that did not work. I tried using activity monitor to force quit, however it did not show up in activity monitor - at least not under the name HP ENVY 7640 series. I tried using terminal to find the PID of the app, but was unsuccessful with finding that either. I am unable to restart my macbook because of this, which means I cannot update anything. Please help.