Thanks! I have wondered what makes "Turn off display" setting randomly change to 20min (mine is set to 'never'). Just happened again today. Googling and reading this topic, i found out that HD Tune does that. I just run HD Tune's Error Scan after some time. And again, reading this topic convinced me that the culprit really is HD Tune. I have version 2.55. It does not have the option to disable this power setting. I guess it's ON by build.