When playing back where is there a signal ? Check routing.
If you are using VST instruments are they turned off. I did this once, it took hours to realise what I had done.
Are channels muted?
If you are using wav files, are they still in the right place. Check the pool
When playing back, you should see indications in the small level meters.
Check the wav files by playing them outside Cubase - Real player or something like that
Check all routing.
Check the VST connections - I know you checked - check again in case something is missed
Make a backup copy - does this work
If you autosave, then check the last save version - does it work ? If yes what happened between this save and the final save.
Open a new project. Make sure it works. Copy one track at a time from silent project and check that it works. You will eventually find the fault, especially if the track is important.