Opened an old project (done with SPLAT) and decided to unfreeze a synth to re-record the part. Only trouble is the synth now will not sound and will not accept MIDI data any more? It does not "see" anything coming in on any MIDI device or interface connected. And I can not open the VST to try and see what settings I have it on to simply re-insert another instance of it. It seems u nfreezing totally blocks it.
 
Any ideas?

You can try a couple things.
1- Try closing and reopening the project. Sometimes this helps.
2- Save the midi and delete the track. Insert the same VST again and drag the midi to the new track.
 
Sometimes its a flaw within Sonar and sometimes its simply a matter of something strange with the hardware and/or the routing. You can also try hitting the midi engine button. Reset it, though im not sure if that will help.