Why are my games running terribly even though it says they are supposed to run fine?

all of that has been tried and it does not make a difference.

Most games will run fine but not 3d intensive games

You need at least a i5

No with that CPU you can do more then ipad

Just not games like cod or flight sim

They'll get 200fps if they've turned off V-Sync. Is your V-Sync off?

Turning of V-Sync (or vertical synchronisation) basically unlocks the frame rate for the game, allowing it to generate as many frames as the system is capable of. This will cause screen tearing though.

If the power supply was faulty, it would manifest as system instability, crashing and shut downs rather than poor performance. You could try fully removing your graphics driver via a free app called DDU.

Best to download the latest NVIDIA driver first and save it somewhere, then run DDU and choose 'Clean and reboot'. When it completes, install the graphics driver. Then try your game/s agiain.

For general performance testing, there is a free program on the Windows Store Called Cinebench R23 which you can use to test both the single core and multi-core performance of your CPU.

Cinebench gives the CPU quite a workout. If your PC crashes or shuts down this would be the sign of a hardware issue.

What games are you trying to play, and what resolution are you running them at? Do you have the display connected to the GTX 1060 or the motherboard?

The i3 8100 is roughly the equivalent of an i5 7400

Have a look at performance videos of the games you've been trying on YouTube. Do they match your performance?

"Can I Run It" should be taken with a grain of salt as many factors can play into the performance of any game including the age of your equipment or other background programs. Trying reducing your settings to the lowest possible and work your way up from there to identify what setting and/or hardware may be causing your performance issues.