Hi Jerry,
I am in the same exact boat. Had the unit for 2 years then it started to do the continuous boot screen restarts. I pulled out the internal SD and found that it wasn't recognized by a Windows or Mac system. Still waiting for a backup img for the 4000nex.
The internal SD card is located below the CD transport on the front right side. See the photo in the link below.
https://www.dropbox.com/s/257feg05qzcc33d/4000nex_SD_Location.png?dl=0