Cleaning PC Hardware on the Inside ...

Off and unplug equipment before you open the case. Use compressed air or a soft paint brush to get rid of the layers of accumulated dust.
Next, especially for those who live in cold countries, touch a well grounded metal object and discharge all the static electricity that could have built up in your hands, before touching any of the circuitry.
Note: Be very careful not to damage the delicate circuitry when you use a brush
Use a vacuum cleaner (if you have one) to get rid of the loosened dust when you use a brush. Always handle circuit boards with a soft touch. Be very gentle when removing and adding them to their slots.
Once finished dusting double check whether all components are attached firmly in place