I have a Cubase 6 project, which has suddenly stopped showing any audio input at all - zero. Hardware and physical inputs are all OK (audio shows as coming in on the system level) other software (such as audacity) sees audio input and I can hear it, even other Cubase projects see audio input and I can hear it, so it must be the individual project - anybody got any idea which button I may have clicked that would do this? - as far as I can see my settings are identical to other functioning projects (e.g. Device setup is the same)
If it´s not showing any audio input, you should check for correct input bus selection of the tracks…!?
VST Connections
yup, checked - same bus inputs as other functioning projects
Wait a minute - what those two guys said is the correct answer. So you need to open your mixer again and make those bus connections. Keep the project up, maybe turn the bus to ‘No bus’ and then turn the ‘Stereo Bus’ on again.
It’s also possible that the Studio Output is engaged and not your Main Stereo Out? Like was said, open your VST connections window and double check yourself. (Typically this will not be your problem because the VST Connections are universal to all projects, FWIW. Still check.)
Yes, checked those - problem is my ‘Stereo in’ meter is showing zero - System prefs audio input shows a definite level, as does a similar Cubase 6 project’s ‘Stereo in’. Device settings is for the correct input - I’ve disconnected everything so ‘built-in’ is the only option throughout.
Hope I can solve this - started trying to export copy/paste parts into new blank project (I thought it would be simple to do, just tedious) but this looks like a can of worms best avoided 
Oh well - I recreated the project as a new file, and copied p/asted over the audio and midi - solves the problem.