Lenovo T450S has screen turn black randomly issue. The screen turns off randomly, but all other modules still work, like key board, video play, .... The screen display can come back when close the lid and open it again, i.e. let laptop enters sleep mode, then wake it up. Or switch display from PC screen to projector or second screen, then switch back. The display in the second screen always work. Until now has not fig out what is the root cause.
Try going into "Control Panel" and then "Power Options". Next click "Change plan settings" next to whichever plan you are using. On the next screen click "Change advanced power settings." Now you want to locate the "Display" settings and check that there is nothing in there that would cause it so shut down. Once you have saved any changes made in "Display" I suggest you check the other sections as well to make sure nothing else is set to shut the display down. When you are done save your changes and see if the issue repeats.
Thanks a lot for Webworkings' suggestion. I already checked the "Power Options" under "Control Panel". The setting for "Screen" off and "Sleep" is 1 hour without any activities with both "Battery" and "Plug in". So definitely it is not the Power Setting issue.
By the way the screen randomly off issue only happens just when the laptop is turn on to about 20~30 minutes. After that, it seems the laptop already warm-up, and the screen will no longer off randomly. I suspect it is hardware issue, but not sure which one: the screen itself, wire connection or the display circuit. I opened the laptop, all connection is fine, have not found anything abnormal. Another thing, the display on the external screen by selecting "Win key+ P" is always fine.
Sometimes my screen display has flickering issue, but all drivers are updated. The original storage is 512G hard disk, I upgraded it to 512G Samsung SSD driver with Samsung software(ghost all files in hard disk to SSD driver) when I bought the laptop two years ago.