Does your computer make a Jet-Engine sound? Does it sound like its working extra hard to do basic tasks?
Dust inside your computer can kill your computer, or at least slow it down.
Dust in laptops:
To remove the dust inside your laptop, you have to take it appart and remove the heatsink from the cpu. Make sure that you put everything back where it was, or have some one that has done this before do it.
Dust in a videocard:
Dust in video cards is really bad, because it reduces the air flow and make a heat producing component burn with its own heat. When cleaning up the dust from your pc, make sure the fans dont spin, as you are cleaning it with a vacum or canned air, they will get damaged.
Make sure your conputer has good air flow, specialy laptops since they produce heat and if that heat is not removed, it will damage your components.