Hi, today my friend used a hair dryer(cold) to blow dust from (or 'in') the back of his desktop pc where the fan is, i mentioned that i believed the hair dryer would simply blow the dust back into the pc whereas a vacuum would at least 'suck' it away, have i got a point?
You will find that, when you are older, such things need not worry normal people. In case you had not surmised, it matters not whether you use a hairdryer or a vacuum cleaner. Dust cannot affect electricity.
Blowing or sucking through the fan will achieve little. Dust sticks pretty hard to fans and would need to be brushed or wiped off. With the side off blowing is safer and more effective than sucking as you do not have to get so near to the components. Dust may not affect electricity but causes the early demise of components through overheating and getting rid of any dust build up is worthwhile,