"system shuts down itself after 5-10 minutes even if I do not do anything. Shutdown occurs with closing all open windows with no messages."
Does the computer shut down completely (as in power off), or does the screen just go black if you don't do anything for a few minuets?
If the power is still on, and the screen just goes black. move the mouse and watch it all come back. The screen saver is probably set to kick in with a black screen.
Go into Control Center -> Appearance and Themes -> Screensaver to adjust things to your liking.