This computer has been opened today for the first time after 5 years. Dust settling is a major problem for fans, and computer health in general. Dust sticks to the grease and accumulates there, eventually interfering with the action of the fan and causing that horrible grinding noise.
Fan problems are by far the most common age-related computer hardware health issue, unless you habitually work in a really clean room.
Common computer fans include the CPU heat-sink fan, possibly the most essential mechanical part in your computer. Problems with this fan can cause all kinds of crashes and software errors due to heat. If that fan stops, so does your computer, potentially forever.
Other important fan is the Power-supply fan at the rear of the case, which is often the only source of airflow in and out of the computer, and any case fans that may have been added to promote air movement and stop the dust from settling.
If you decide to clean the inside of the computer of all visible standing dust using compressed air be sure to hold the can as close to vertical as possible to prevent liquid spray that could harm components.
