MacBook Unibody acting weird!

My macbook unibody is starting to act very weird.

I brought it to some computer guy and he said its the hard drive.

But I don't think its just that, because it still works! just freezes after a little while.

So heres whats happening, I'm on it and after about 20minutes, the fan gets really loud ( I've never even heard the fan on before ) the computer is not hot at all, and then my mouse freezes and nothing happens and it just stays frozen forever, I have to hold down the power button and shut it off.

OR it does this

It works perfectly fine, my internet starts getting slow, and it hear the fan get louder, I go to click on my Airport icon to see if I'm connected to the right wifi, and it will freeze, that happened atleast 5 times. And last night the wifi said : no hardware installed but after I restarted the computer it was fine.

It deleted alll my iPhoto pictures and I can't recover them at all . ( if anyone can help with this please help me. 2 years of pictures gone. )

( I've never used time machine and don't know how so. )

Please someone help me I don't know what to do

I bought this computer refurbished and it was perfectly fine until now. it literally happened over night, I shut my computer off and the next morning I went on and this was happening.

Someone told me it could be dust in the fan getting clogged and that I should but the end dust spray?

Anything will help thank you ahead of time.

btw, I ran the smart test, and it passed..so I don't think its the hard drive!