Solved! Display setting of Dell ST2420L monitor going black after few seconds!
This is weird. I dug up my closet and pulled out my old Dell ST2420L and plugged it in. It was turning off after a few seconds! Sucks!
After an hour of changing cables and input devices ... here is what worked!
During the few seconds that the monitor was displaying ... I turned the brightness level close to zero! That's it! The monitor go off anymore!
Apparently as mentioned here by Plato1123:
If your LCD display is turning itself off due to aging capacitors, an easy work around is to turn the brightness down! Brightness goes down, display draws less juice, and you can at least use it. As it warms up you should be able to gradually turn the brightness back up, although probably not all the way.
Sometimes this problem manifests itself as a display that turns itself off after a few seconds or will turn itself off and back on over and over again.