FX-4300 and GTX 1050 odd performance lag

Feb 5, 2019
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When first I bought the GTX 1050 2GB to team with the old FX-4300 everything runned just fine. It was mid 2017, if I remember well. From the mid 2018 to today, I feel like the gaming performance dropped a lot.
I really don't know if the FX-4300 that I bought at the start of 2013 is giving up or if it is just an odd bottleneck, since that games such as Modern Warfare 2 (2009) runs with low fps (35-40 with all maxed, my resolution is 1366x768) and games as Battlefield 4 (2013) runs just fine, with some limitation in fps due to the old cpu (runs, at high setting, with 60-110 fps depending on how many players are in the match).
Just one more odd example: If I disable every effect on MW2 the fps increases greatly, leading to a cpu suspicion.

My specs:
Motherboard: asrock n68-s3 fx
Graphics card: Geforce GTX 1050 2GB
Processor: AMD FX 4300 3.80Ghz
OS: Windows 10 Pro, just installed
RAM: 2x4GB, different Mhz. I think that both are Kingston

I have tried:
Changing OS, had the W7 before;
Resetting BIOS at the Motherboard menu, don't know if hard reset would've worked better;
Installing latest graphics drivers.

Have not tried yet:
Changing thermal paste – Don't know if that would help...

I really don't know what caused this issue and since I don't have money to spare I hope that I can get to learn something with you guys.
 
I updated the Motherboard BIOS but the game still runs the same. I can't tell what causes Modern Warfare 2 and Far Cry 3 to run low fps, but I tested the fresh installed PayDay 2 and it runs beautfuly. I also ran some tests monitoring CPU temperature while gaming, it did not get much beyond 70ºC with BF4 on Ultra, there is nothing relating the temperature to low fps on my computer.

Thanks for the advice, I really, really appreciate your help.