from the first time i buy my pc to the first time i actually open my casing, there was not much dust.
after i open my casing due to heat problem, dust starts buidling up..

until on start up , my old p4 2.4 reaches 50C. just bit of w3 , it goes up to 60C. in the end, i remove the heat sink, remove the fan from heat sink, clean it with water , clean the fan with tissue, attach back, clean the contact area, put new termal paste, attached back the stuff, let it run.. temp goes down until 37c on start up, and nver goes more than 50c..

still open till now... my p4.2.4 is history, got a p4 2.6. the casing is open and being blown by using a table fan.

one thing i notice, if using a table fan, the heat sink fan actually lowers it RPM automatically..