Low fps problem.

I am wondering why my game runs at such low fps even though I have a decent system. I read somewhere that apparently old cpus just dont do too well. I found that quite odd since I am running a Phenom II x4 964 oc to 4ghz no less and a gtx 780 but only get 20-30 frames with creations over 200 blocks. If anyone has any idea how to fix the issue or just any tips please message me.
ok? well the cpu seems ok, but a 780 is quite old. we are already at the 20xx(11xx) series after all.
and amd is generally not that well supported by the unity engine, when i used a amd gpu way back i couldn't turn on shaders because it would bug out the game.