I have an HP Pavilion g7 NOTEBOOK PC I bought last year.  I upgraded to Windows 8.1 a couple of months ago and I have had problems EVER since.  The issue I am trying to solve now concerns online videos.  When I am watching videos streamed online in full screen mode, it will pull out of full screen without me touching the keys or mice.  I have noticed sometimes the bar at the top of the browser screen flashes, as though another program is trying to open.  I just took it in to a computer REPAIR shop and they said they removed several viruses.  They advised me to download avast and malwarebytes, and I did.  Then I started a video, and about seven minutes in it popped out of full screen.  I never used to have this issue.  I would like to know what could be causing this, and if there is a setting I could find that would stop a new window from taking a video out of full screen.  It happens on many websites, and I have tried using Internet EXPLORER and Google Chrome.Do you have HP's software tools such as HP Utility Center, HP Support Assistant, etc. installed?  I believe this software is normally installed on all new HP computers.  So, you should have it unless you removed it. 

I have an HP Pavilion g6 Notebook PC and I've found their software to be helpful in updating device drivers.  Perhaps driver updates, such as the driver for your Display Adapter, might be helpful in resolving your issue. I do have HP Support Assistant.  I have tried reinstalling drivers, reinstalling all programs, even took it into a repair shop.  The shop removed viruses, but I still have the issue.  I'm wondering whether accidentally touching the touchpad might be the cause of this.  Do you know how to disable the touchpad?  Try disabling it and see whether the problem continues.