If your computer is running slowly, if your PC fans are noisy, or if you’re experiencing crashes and poor performance, it may be that your computer is just a bit dusty.
Clean Out Your Computer Day is an annual reminder to open up the casing (turn off the power first!), and to give everything a good, careful clean out.
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All details taken directly from provider content at http://www.daysoftheyear.com/days/clean-out-your-computer-day/