System - NT Kernel & System - High CPU Memory

[BuBu Shofronea]

Since i've bought my GTX 750 OC 1GB i'm having this issue with my computer. When i do start a game and play it for like 3-5 mins, the pc starts to go crazy. The FPS drops from 40-50 to 15-18, the browsing goes really really slowly ( especially when i want to open a new app ), internet browsing aswell... Only after 12-15 mins, my computer goes back to normal.
So i've checked the Task Manager and clicked on the CPU bar from the highest to lowest and i saw that a process called System is taking almost to 100 of my CPU memory ( the CPU valor goes to 100 ). Also another process called System Idle Process is doing the same ( even after restarting my computer it's still on 50-90 ). I have no ideea what caused that and i really want a solution.

Specs :
CPU : Intel Pentium Dual Core @ 2.5 GHz
GPU : Asus nVidia GTX 750 OC 1GB GDDR5
RAM : 4GB DDR3
MB : Foxconn G31MX
PSU : 450W

 

[Pinhedd]

Since i've bought my GTX 750 OC 1GB i'm having this issue with my computer. When i do start a game and play it for like 3-5 mins, the pc starts to go crazy. The FPS drops from 40-50 to 15-18, the browsing goes really really slowly ( especially when i want to open a new app ), internet browsing aswell... Only after 12-15 mins, my computer goes back to normal.
So i've checked the Task Manager and clicked on the CPU bar from the highest to lowest and i saw that a process called System is taking almost to 100 of my CPU memory ( the CPU valor goes to 100 ). Also another process called System Idle Process is doing the same ( even after restarting my computer it's still on 50-90 ). I have no ideea what caused that and i really want a solution.

Specs :
CPU : Intel Pentium Dual Core @ 2.5 GHz
GPU : Asus nVidia GTX 750 OC 1GB GDDR5
RAM : 4GB DDR3
MB : Foxconn G31MX
PSU : 450W

You can ignore the System Idle Process. This is the process that runs when the microprocessor has no other work to do at the time. How old is your hard disk drive?