Frames per second fluxuations

So basically heres the problem: frames per second fluxuations. I have a clean pc, freshly updates and scanned with norton antivirus. it has been set up so the game is uneffected by norton.

So heres what happens in game. i have a usual frames per second of about 50-70. Lately however, the frames per second decides to drop to 0.7 randomly, freezing the game. I have already used game booster, which helps to decrease the frequency of this happening, however it continues to drop below 0.7 frame per second.

Please help solve this problem which has been plaguing me for over a month!