XPS 2720 AIO, screen off for 2 seconds then on again
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Does it keep going on/off or does it stay on after the first time it turns off?
Version of Windows? If Win 10, did you recently update to v1909?
What color is power button when screen goes off? And steady or blinking?
If using a power strip or surge protector, remove those and connect PC to working outlet.
You have an HDMI-OUT port on rear of PC (#17, here - NOT #22). Connect an external HDMI monitor to that port and see what happens.
Forum Member since 2004 I am not a Dell employee