Question Computer lags and crashes when in full screen mode while gaming

I have a problem with my new pc build, it worked fine for about 2 months since I bought it, played games perfectly and it worked great without any problems.

One morning, it randomly started crashing, the screen will go black and the pc will "hung" and requires a manual restart while working with Photoshop, video players. Playing games worked without issues.

So I formatted my drive and did a clean windows 10 installation. Now all my programs work perfectly and the games worked fine until about a week ago.

When I open a game such as Battlefield 4, Ghost Recon Breakpoint or even Minecraft, the game will lag extremely bad, but the FPS monitor counter doesn't drop to any low frame rates in any game while it lags, the fps is constant.

When playing games with the stuttering and lag, the computer will freeze up to a black screen, with my monitor light flashing after about 5min and sometimes immediately after the game loads. This is in full screen modes for all games. Also using alt-tab makes all games unresponsive although, there's still sound and I need to end the game process with task manager. As the game will only return to a frozen state with a cursor displaying.

My cpu temperature is in the 50 to 60 degree range when playing Battlefield 4 on Ultra settings and GPU is between 60 to 70 degrees. I also tested a new 750W Corsair PSU and an Antec 750W PSU, did many memory tests without any errors using windows diagnostic. Added new thermal paste to the CPU and rechecked all the component connections and cleaned out the computer of any dust there might be. Also, I clean installed the latest video drivers after a clean OS Installation. Yet the problem remains.

I clean installed windows 10 again today on a new SSD drive without any software except for all the latest video, chipset and device drivers. Now I can do my work, all programs, such as adobe, VLC etc work fine but games still lags and freezes my computer when in full screen modes. When I switch to borderless mode, the games perform without any lag/stuttering and I did not reveive a pc crash after playing 2 hours in borderless modes, full screen freezes up the computer after a few minutes.

I did a stress test to monitor CPU temps and also ran Firestrike benchmarks and there were no lag or crashes during the tests with GPU temperature being on 70 to 80 degrees in some of the benchmark tests. Scanned my system for malwareband also made sure the latest Direct X and .net software are installed correctly.

This is a bit of an inconvenience and I would really ask for any assistance to this problem. My sincere apologies for the long post.

PC specifications:
Msi X470 Gaming Pro motherboard (latest BIOS)
AMD Ryzen 5 3600 (stock clocks, aftermarket fan cooler)
AMD RX5700 (reference model, latest adrenaline driver)
Corsair Vengeance 16GB DDR4 at 2666Mhz
500GB Samsung EVO 850 SSD
Antec 750W PSU 80Plus
Windows 10 build 1909
 

Lutfij

Titan
Moderator
Antec and Corsair are brands while 750 is the wattage from the PSU. You will need to mention the model of the PSU. Can you please state which BIOS version you're currently on? Did you recreate the installer for your OS using Windows Media Creation Tools?
 
The current PSU I'm using is an Antec HCG750 750W High Current Gamer Gold Series Power Supply. The other PSU tested from my other computer is a Corsair RMx Series RM750x 80+ Gold.

The BIOS version is:
7B79v1E

I installed a licensed copy of Windows 8 from the provided DVD on a new SSD drive and used Windows Media Creation tools to update to Windows 10 Pro.
 
Today I played and tested battlefield 4 in bordeless mode, for about 3 hours without any lag or system crashes. I set the graphics on ultra and the resolution scale to 200% and my GPU was on 77 degree Celsius and CPU between 58 and at times spiked to 70 degrees after the 3 hours. As soon as I've changed the settings to full screen, the computer immediately crashed and froze to a black screen. With minecraft, I tested it for about one hour in bordeless mode, it also did not stutter or crash. Changed it to full screen and it lagged extremely bad to a point where it's unplayable. I placed the GPU in my other computer and played battlefield 4 on the same settings in full screen without any crashes, less fps due to the other system which is only an old intel i7 2600k. I'm no expert. Can anyone please give me advice on how to start testing for the culprit component or software which might be causing this?