Vulmaro :
s4in7 :
No, you won't need to reinstall Windows unless you're experiencing errors. Changing a CPU or GPU rarely requires anything like reinstalling Windows.
Even though I try to play a GPU based game, there is not even 1 fps change. I have gtx 760 with 2x4 gb corsair 1600mhz ram
If you play a GPU intensive game, it will put more load on your GTX 760, not your new FX8350. Therefore you won't see much FPS increase.
I'm also not understanding your original question. Could you reword it? What I gathered is that you used to have an old phenom processor and you upgraded to the FX8350. This means you bought a new motherboard. You didn't specific if you're trying to use the same hard drive you used with the old hardware. If you are, you need to reinstall Windows, I believe. (If you're using the same hard drive and you change motherboards, reinstalling is needed.)
Don't quote me, that's just what I've heard.