Which procedure is recommended when cleaning inside a computer? Clean the hard drive heads with a cotton swab. Hold the CPU fan to prevent it from spinning and blow it with compressed air. Remove the CPU before cleaning. Invert the can of compressed air while spraying.

Hold the CPU fan so that it won't spin and blow this with compressed air.

Explanation:

While cleaning the computer system from the inner side then we have to follow some steps.

only #2 represents an object at rest on a table.

in #1, there is no normal force due to the table; the object is accelerating downward.

in #3, the vertical forces are not balanced; the object is accelerating downward.

in #4, neither the vertical nor the horizontal forces are balanced. the object is accelerating upwards and to the right.