Middle C is softer than every other note. It occurs only on some instruments. A lot of the instruments sounds slightly different than they used to as well. It's happened before, but righted itself somehow. Now, two years later, it's happening again. Is this a problem with my cpu, or did I accidentally do something to the noteworthy software?
There is not the doing of NWC. There is no option that would only have an impact on one note pitch.
If all your instruments sound different, an unlikely but possible cause is an incorrect midi playback device selection. Check it at Tools, Options, Midi.