Gigabyte Gpu GTX 960 suddenly too slow for dx9 games

All of a sudden, games using direct X 9 are too slow and stutters with around 10-20 fps, while the gpu is working at 99%. The exact games used to function a week ago reaching 100+fps and without that stress on the GPU.

The Nvidia experience says that I can play these games on max settings, which I have always done for years. But now it feels like my pc got senile all of a sudden.

The paradox now is that newer more resource demanding dx11 games function perfectly as they did, nothing has changed! And on some that have the option to, if I chose to play using dx9, fps drop down to the ground!

Games:

• Call of duty MW2 and MW3 the old ones from 2009 and 2011. (Used to run like a charm, now unplayable at 11 fps.
• Call of duty ww2 (surprizingly still working perfectly as before)
• Max Payne 3 works perfectly when set to use dx11 but too slow on dx9!

Tried all the below with no success:

• I formatted my drive and installed a clean windows setup.
• Cleaned my pc components, ram, gpu, cpu, fans etc.
• Flashed an updated version of BIOS.
• Tried not installing any windows updates.
• Tried older versions for my GPU drivers.
• Made sure directX is updated, and all other needed drivers are installed.
• Reinstalled the same games from scratch.
• Used pc passmark benchmarking tool to put heavy stress on all pc components, nothing failed. However, it pointed out that its dx10 and dx11 performance is in the same range as other user PCs with the same setup, BUT dx9 tests show that the performance is way down even worse than an intel HD4000 and a gt 640!

Pc

• Nvidia Gigabyte Gtx 960 2GB
• Kingston A400 ssd
• Intel Q9550
• 8GB ram
• Windows 7 ultimate (same copy)

Solution 1:

Ok, so after 3 weeks of going in circles, today I took out the motherboard battery and disconnected the power cable and made sure all charge has been discharged.

After putting the battery back and booting, it booted fast like before and all games now work perfectly as they used to.

Tbh, this is so strange as I already tried flashing the BIOS, resetting CMOS to load fail and optimum default settings, tried my custom settings etc. And why was this issue only visible with directX 9 games only?!

Anyways, that's how I solved it in case somebody gets such issue in the future.