If you are experiencing the Proteus screen flashing on and off roughly every 5, 10 (default), 30 seconds, or consistent interval.  Check the the HDMI source on your video app.  If it is set to "Alternate" change it to whichever source you have Proteus plugged into, for example "HDMI 1".  Go to and press the "Options" button in the bottom right corner of the screen, then press "Source" to change it to the proper source.  In this situation   "Alternate" means to alternate screens in timed intervals.