Quite topical with the hot weather we are having in Berkshire, but have you notice the fan running on your laptop or computer all the time? Is it noisier or running hotter than when you purchased the computer? It probably is.
Your computer needs to pull air through itself to stop overheating. As it pulls that air through dust particles get stuck in the heat sinks within the computer, reducing their effectiveness This in turn leads to the computer running hotter and the fan running faster. In extreme cases the system may shut off when it gets too hot.
A simple solution is to blow some compressed air into the unit, or hoover it out in order to remove the dust.