I have my Win 7 Pro 64-bit desktop set to display the password screen from the screensaver whenever there is mouse activity. I also have the display turn off after 10 minutes.
However, a few weeks ago this started behaving weird. Sometimes the password screen would appear, other times I'd go directly to the desktop. Sometimes the display would turn off, other times it would stay at the desktop. Sometimes the display would turn off and then turn on in the middle of the night.
I've run sfc /scannow, run the recovery disk, checked the local security setup in the administrative tools, run MalwareBytes, and everything seems to be set correctly.
I'm including a copy of the latest dxdiag if that helps.