High CPU all of a sudden!

[Amored]

Hey. I've been having issues with my CPU load during games lately. Take Dota 2 for instance: I've been playing it a lot with quite stable framerate, but lately it's unplayable. My PC is quite dated, but it shouldn't really matter in a game like Dota 2. I have a i5-750 and a GeForce 560. I know it's nothing special, at I've never had any trouble playing anything other than the newest games which don't really interest me. So, I start up the game and play it for a couple of minutes until the framerate goes terrible, and the CPU load is at 99%.
What is the issue here? Is my CPU broken? Is my motherboard broken? How can I diagnose this?

 

[Supahos]

Check CPU temp. Guessing it's getting hot and slowing down.

 

[Amored]

I checked in SpeedFan.
GPU: 30C
Temp1: 70C
Temp2: 80C
Temp3: 25C
HD1: 30C
HD0: 30C
Core 0: 70C
Core 1: 70C
Core 2: 70C

So it seems there's an temperature issue in there. But I'm not sure any of these are the CPU.

 

[Amored]

I have solved the issue. I spent a long time thoroughly cleaning just about every part of my computer. Now it works as well as it did 3 years ago. Thanks to Supahos for the advice!