In 2012 I wiped the HDD drive on a HP Pavilion g7-1322nr laptop. I got rid of Windows and installed MX Linux the latest edition of which was installed just 4 days ago by me. When I quite infrequently use this computer, things seem fine 'til I go away from the laptop to do something else. While I'm away from it, the screen goes blank (but not black, so it's still running) and is locked. Nothing I do - save restart the laptop - gets me back to a useful desktop. What could be wrong here and how is this fixed? Is this some kind of flaw in this model?