Weird FPS Issue

[CaolanD]

i play most of my games at 60fps constant but sometimes when i play after a certain length of time my game suddenly drops to below 10 fps and it stays like that until i either restart the game or set its priority at high. if anyone can help with this problem i would much appreciate it.
Thank you in advance
List of PC Parts:

• 
  GPU- MSI GTX 970
  CPU- i5 4460 RAM
  RAM- Hyperx furys 2x4 GB
  Motherboard- msi z97 gaming 3
  

 

[KR2]

You could try to make it so that the game always opens and stays at top priority. You can find this here. - The source is from WikiHow.com