I am very new to this, and my c9 terminal seems to be frozen. The cursor is blinking, but when I try to enter text, nothing shows up. I have tried exiting my workspace and reloading and it still will not work.
Opening a new terminal tab with the View menu or pressing ALT-T is the best bet to get a working terminal back (as mentioned in the comment above)... you may also find that having selected the broken terminal though, you can't click things in your menus anymore. I've found that pressing the Preview button and then closing it, seems to get the UI to be responsive again.
Supports official response is that you should perform workspace reset using ?reset=1 after your workspace url (which doesn't last or work very well in my experience).