Does this happen when there is nothing on the screen (i.e. when there is a black loading screen in a video game)? If so, it could be because the monitor has power save mode and automatically turns off if nothing is detected on the screen.
The VS238H-P dims when there is (expected)...the VG248QE doesn't (don't expect it). The VG248QE just turns off/flickers randomly no matter what I'm doing.