Hi Patti
Glad you are enjoying your DGX660. I have the same instrument.
The menu is extremely extensive, and you can tune every single aspect of every sound, including microphone settings. But be careful when using it, because as you have found, it's too easy to disable something!
Should it happen again, a failsafe method,is to return the DGX to factory settings. To do this, with instrument turned off, hold down the highest white key, and turn on the power button. Continue to hold the key down until you get a message in the LED display.
Your DGX will now be all back to normal. You will lose any settings you've changed of course.
Hope you enjoy your instrument, I have been blown away with mine, and have learned a lot from the many YouTube clips now freely available for it.