Hi I renovate old radio's & TV's as a hobby. Frequently they are covered in layers of dust & gunk after years of service. Rich has it pretty much spot on, and I clear dust in a simllar way. I use a paint brush and an old vacumn cleaner (with the hose attachment) to clear out the dust, as I am brushing it away. I would concentrate on areas around the CPU and power supply fan intake. In general this works a treat. If the PC has been used in a smoking environment then the Nicotine & Tar can cause the dust to coagulate and form a thick gooey mess. I doubt you'll find this as it takes years to build up. Getting rid of the Nicotine & Tar & dust mess is not so simple, it can be done, but does involve additional cleaning fluids and care. If you need to do this, I'll help if I can. Regards Adrian (FJ)