Have you put your device in a case recently? I had issues when I got my case because the volume buttons are togeather, and because it's made of a fairly firm silicone, pressing one button the right way tends to slightly press the other. Sometimes I need to remove my device from the case to take a screenshot. Also, how old is your device? If you aren't using a case, and you've had the device for a while, the buttons may be wearing-out...Hi - In the past I've been able to take a screen shot by holding the Vol. Down and Power buttons simultaneously but that no longer works.
Those keystrokes do nothing now.
Any ideas why?
Android version 5.1.1