FPS drop After a few minutes Playing

[Meow Meow]

This issue has occurred since a month ago. When i begin to play any game like Assassin's creed 4, BattleField3, Total War: Shogun 2,... it runs smoothly (50-60fps) in just 5-10 minutes and high setting... Then randomly, the FPS drops like hell (10-20 fps, lower in AC4)... Sometime, when i restart the game or change resolution, it will get back to normal but sometime it will need to restart the laptop... So i used GPUZ and test with Saints Row 4 to see if my GPU still working or not, and this is the result.
+Normal: http/s11.postimg.org/43sho1uzn/image.gif
+Issue Occurred: http/s11.postimg.org/l9f56efc3/image.gif
This is my Specs:
+Asus P550L series
+CPU: Intel Core I7-4510U 2.00GHz (4Cpus)
+Intel GPU: Intel Hd 4000
+Nvidia GPU: Nvidia Geforce GT840M
+4Gb Ram
+Windows 8 Pro 64-bit
And As you can see in 2 gifs above, Temperature (50-60C) is not high enough to think about Overheating so dust can't be my problem here. And my default GPU set as Nvidia one... Hope someone have the answer soon and help me to solve this problem... And sorry for my bad english too... ^^

 

[Dunlop0078]

Whats the cpu temp? It definitely sounds like thermal throttling to me.

 

[Meow Meow]

Whats the cpu temp? It definitely sounds like thermal throttling to me.

sorry, i forgot about Cpu.., Cpu temp is around 45-50 when idle and 60-70 when full load...

 

[Dunlop0078]

Now that i look at it more close, when the issue occurs the gpu is at 135mhz it should be at 1124mhz so its definitely downcloking itself a lot but i dont know why it would do that at 55c. Use msi afterburner to see what the max temp the gpu gets to before it starts to throttle.

 

[Meow Meow]

Now that i look at it more close, when the issue occurs the gpu is at 135mhz it should be at 1124mhz so its definitely downcloking itself a lot but i dont know why it would do that at 55c. Use msi afterburner to see what the max temp the gpu gets to before it starts to throttle.

the highest temp received from Afterburner is 61C...1 month before, when this issue hadn't occurred, whenever my Nvidia Gpu full load, temp always in 60-70... dont know how it get to that low temp this time...

 

[Dunlop0078]

Now that i look at it more close, when the issue occurs the gpu is at 135mhz it should be at 1124mhz so its definitely downcloking itself a lot but i dont know why it would do that at 55c. Use msi afterburner to see what the max temp the gpu gets to before it starts to throttle.

the highest temp received from Afterburner is 61C...1 month before, when this issue hadn't occurred, whenever my Nvidia Gpu full load, temp always in 60-70... dont know how it get to that low temp this time...

I dont know thats strange the gpu should not be throttling at 55c but it is. Are your vents blocked with dust? try to blow it out with a can of compressed air.

 

[Meow Meow]

Now that i look at it more close, when the issue occurs the gpu is at 135mhz it should be at 1124mhz so its definitely downcloking itself a lot but i dont know why it would do that at 55c. Use msi afterburner to see what the max temp the gpu gets to before it starts to throttle.

the highest temp received from Afterburner is 61C...1 month before, when this issue hadn't occurred, whenever my Nvidia Gpu full load, temp always in 60-70... dont know how it get to that low temp this time...

I dont know thats strange the gpu should not be throttling at 55c but it is. Are your vents blocked with dust? try to blow it out with a can of compressed air.

Nope... I dont think dust is the cause for my problem... I remembered i had cleaned out dust 2 months ago with a vacuum...

 

[Meow Meow]

Finally... I Solved this Issue myself...=.=... It's GPU driver that caused that issue... All I had done to fix this is just completely uninstall Nvidia Graphic Driver in "Programs and Features", restart my laptop then Download and perform a Clean Install that driver in "NVIDIA geforce experience"... When complete... Restart it one more time... And Now I have played Saints Row 4 and Pes 15 for about 7 hours without surfering any Fps drop... Anyway... Thank Dunlop0070 for your advices...^^