Second monitor turns blue problem I have recently upgraded to an iMac (Retina 5k, 27-inch, 2017) that has High Sierra (OS version 10.13.3) installed. I have an Asus monitor that I used with my old iMac and had no issues. Ever since the upgrade (usually not more than once a day), the second display will suddenly turn blue:



The only cure I've found is to disconnect the screen and reconnect it. Another similar problem I have with this computer is that my headphones are not recognized all of a sudden and I have to unplug and re-plug to resolve this.

I have a feeling there is some sort of software glitch as both the monitor and headphones worked well on the old computer. I would appreciate any help resolving this.

Update:
Ever since I've reset my SMC 2 days ago, I haven't seen the "blue screen" (thank you @howdytom), but I am still not sure that this a permanent solution. As I am using a cable that was given to me by the IT department, I am not exactly what adapter it is. But here is a picture of it:



BTW, after I disconnected the cable the headphones were not recognized again and I had to plug and unplug them.
You can try to reset the SMC on your iMac


Shut Down your Mac
Unplug the iMac form the power cord.
Press and hold the power button for 5 seconds
Plug the power cord back in and turn on your Mac.


Also, you can try to reset the NVRAM


Shut Down your Mac
Press the power button and immediately press and hold these keys together: Option Command P and R
Keep these keys pressed down for at least 20 seconds until you can hear the startup sound again
You can release all keys after the Apple logo shows up and iMac boots normally.