Hi Denn,
in this case you would not have needed a Reset or reinstall the operating system. It happens again and again that the Transposition of the instrument is changed by Registrations (e.g. when using unknown Registrations, or because you have simply saved "wrong" transpose settings in one of your own Registrations).
To check which Transpose settings are currently set, just press the "MIXER" button on the S670 (the "MIXING CONSOLE" button on the T4) and go to the "TUNE" tab. Here you make sure that under "TRANSPOSE" all three parameters (MASTER, SONG and KBD) are set to zero.
Then press the EXIT button to close the Mixing Console display.
I also recommend checking the following setting: Press the "Direct Access" button and then the "TRANSPOSE -" button to call up the "Transpose Assign" display. Here you make sure that this parameter is set to "KEYBOARD" (NOT "SONG" or "MASTER"). You can use the Panel TRANSPOSE +/- buttons to set the transposition of the keyboard directly. (To reset the Transposition back to zero, simply press both TRANSPOSE buttons at the same time.)
Press the EXIT button to close the Transpose Assign display. This will also automatically save the setting in the System Setup.
It is best to save your preferred settings in at least one "Setup Registration". Be sure to have ticked all needed checkboxes in "MEMORY" dialog (at least SONG, STYLE, VOICE, HARMONY/ARPEGGIO, TEMPO and TRANSPOSE). To be on the safe side, you can also just tick ALL checkboxes when saving such a "Setup Registration". If an "error" should occur later (such as the current problem with the Transposition), you can reset the instrument to a defined state by simply calling up such a Setup Registration.
Hope this helps!
Best regards,
Chris