XPS 27 All In One Shuts Down When Idle

My computer shuts down  when idle. It does not shut down while I am using it   The screen is set to blank after 10 min and the system is set to sleep after 20 min.  It seems to be shutting down after 20 min rather than sleeping, Normally at night I shut down and let the computer sleep,.waking it up with the mouse.  I have had a several instances of disk errors of late requiring that I let the PC do an automatic repair of disk errors upon reboot.  Crossing my fingers that seems to be less frequent but.........

Things I have done:

Performed a backup and recovery to a known good image using Acronis.  Problems first started upon noticing the computer shut down on its own. Upon reboot the automatic repair proceeded slowly and when completed windows  booted however run time errors necessitated a restore of the OS. No more run time errors now.

• After recovery I ran the Dell diagnostic suite which passed.
• Disk cleanup performed
• Computer seems fine when I am using it.

I want to assure myself that this will not be a daily ritual!

Bill Garrison