Always remember to have all your computer fans cleaned once every 3-4 months. If you see on the screenshots there are 3. One shows the computer speed, the other two are before and after cleaning. I ran Prime95 to stress the cpu @ its 4.5ghz overclock. You will see that the temp difference is as much as 7 to 8 degrees per core in this situation and this is MY computer. I last cleaned it about 6 months ago, now imagine if it wasn't cleaned in over a year. You could be running your PC much hotter than it needs to be at.
Note to those wondering this is an i5 2500K normally @3.3ghz, I have it overclocked to 4.5ghz.