You've got something very odd going on here. MIDI through simply allows midi coming in, to be sent out again - and for a lot of people, turning it OFF is vital, because with an external keyboard connected, you press say C1, it sounds, but then Cubase sends it back to the keyboard a fraction of a second later and it sounds again - creating double notes, and even worse, some keyboards also have midi thru engaged and send it out again, and every note you play records two! If you create a VST instrument and then use the MIDI output routing too play it, you may need thru on. On my system - you do NOT. If you create an instrument track, then again MIDI thru is not needed, because you do not want the output sent anywhere.
Has this instance of Cubase ever worked properly? None of these problems are common, so it suggests either the installation is badly mangled, or somehow you have done something. The MIDI filter section is something you shouldn't need to fiddle with unless you want things to be done slightly differently, or need to filter out continuous data that either chokes a busy feed, or causes timing issues - stuff like that. I do use it for some things but that's just because a couple of external synths are very picky. Using only internal VSTis you wouldn't;t normally have these issues.
So -
has it ever worked playing internal sounds?
Do any of the internal sound work (I think you said no)?
Both instrument and ordinary MIDI tracks no not record any data at all when you hit record, but the midi activity meter says midi is there?
One thing you can try to move us along.
Create a MIDI track manually - so you have MIDI data absolutely there! Create a few bars of a new midi track, double click it to open the editor and enter random notes with the pen tool - any old rubbish will do - then see if this can be copied and pasted to an instrument track and produce sound.
Report back.
