That is NOT ... a complete list of your system, lol
Make/Models of motherboard, type of cooling, power supply, case, version of Windows ..etc
You have a pretty old setup .. 4core/4thread CPU with mismatched DDR3
You haven't listed any troubleshooting steps you might have done
You haven't mentioned if system WAS working ok and now all of sudden it's not or any surrounding circumstances prior to your issue manifesting itself
Is you issue with just games .. just certain games .. or do you get mouse stutter in Windows too?
Is AHCI enabled on your SATA controller in your BIOS? That setting CAN make a huge difference on older DDR3 era setups with gaming
IF you just got this GPU and installed it, did you run the program called DDU to remove all driver residue from whatever brand (AMD or Nvidia) GPU's you were running before on this install of Windows?
How are your CPU/GPU temps?
The more info you give, the less we have to guess
Have you checked your systems Event Viewer for logged errors that might indicate some kind of issue on your setup?
