I am sorry you are having this problem but let me help you.
The situation you are facing with the system is weird but the troubleshooting steps you have done are very good and you have identified the issue.
By testing the computer with the onboard graphics and onboard audio let us know the Intel® graphics is not the problem but the discrete graphics driver you have. Based on that, I recommend you checking for firmware updates or driver updates for the video card. Another good step is to check for BIOS updates for your motherboard:
Here you can get the latest driver for your video card: