Ctrl+Shift+S now locks the computer

[Weboh]

I use Ctrl+Shift+S for years as a shortcut in Word for strikethrough. Yesterday, that shortcut started locking the computer. I have no idea why. I didn't install anything or mess with any Windows settings yesterday, nor can I find anything online about that shortcut locking the computer.

Also, my computer has taken to locking by itself at random other times while I'm using it. I can't find out what causes this either, nor can I consistently reproduce anything that does it.

A little help?

Thanks.

 

[Ranger4]

Check that your Caps Lock is not on.

 

[Weboh]

Both ways it does the same.