S2417DG, cannot enter FSM (Factory Service Menu) ?

Hi!

My Dell S2417DG automatically turned on BurnIn mode. Whenever I try to access the FSM by pressing the first, second, and power buttons to turn it off, the S2417DG goes black and will not show the display anymore. I have to unplug the power cable to get it to show my display again. How can I fix this?