If it's really dusty take the computer outside the house, some of the canned air is not good to spray a lot of it inside a closed area, it's not good to breathe it or the dust.
Try not to turn the can upside down it releases the liquid, the liquid won't hurt anything it's a quick evaporate, but you'll loose some of the pressure.
Short controlled bursts spaced out will keep the can from freezing up on you.