In cases like this, it's best to troubleshoot by eliminating possible reasons, starting with the simplest. I'd do the following:
- Check that you didn't accidentally change the global MIDI channel on the Virus. Switch the Virus to Multi mode, maybe some other channel will respond.
- Make sure your MIDI keyboard is working and sending on the correct MIDI channel. Connect it to another synth/module if you have one, or connect it to PC and use a MIDI monitor software like MIDI-OX.
- Connect your keyboard directly to the Virus, let's take PC out of the picture. When you play the keyboard, does a note symbol appear on Virus' display? If yes, this means that MIDI in is working, and the problem is somewhere else. If no, try another MIDI cable, and if that doesn't help either - well, maybe MIDI input is indeed broken.