To summarize:
1. Please use resolution of 1920x1080 (full settings or your confortable settings ) and check your CPU usage, and tell us here about it.
2. Run Malware Bytes to scan your entire PC, and clean whatever you find.
3. Install a proper Antivirus (Microsoft Defender is not good). I personally have ran about 4 years with AVG free (don't install browser extension or any other addon, even if it's from AVG).
Now I have bought AVG Ultimate for 1 year (so I really trust this antivirus from protection and usage perspective)
4. Re-Install the latest official drivers from manufacturers (not the ones from DVD / CD) (DO NOT TOUCH THE BIOS DRIVER)
For your motherboard ( First install ".NET 4.5" and second install "Intel Management Engine Interface"): http://www.gigabyte.com/products/product-page.aspx?pid=5485#dl
For your Video Card: http://www.geforce.com/drivers/results/110603
Please check to see if you have Windows 10 on 64-bit.
5. If the problems persist, I can help you over a remote desktop solution like TeamViewer (used in non-comercial purpose it's free)
My help would be at no charge for you
The bold letters should be respected without any exceptions otherwise it will cause undesired behaviour.