Abnormal Fan sound

Hey everyone, I have something that just recently happened today. I'll go threw a whole story so you'll know everything!

Well I have a Compaq Presario C700. This computer is known to have a pretty noisy fan. Well, the laptop starts up with the fan running for about 2 seconds, then starts up, usually mine is really noisy when it starts. Then it's quiet until I move my mouse and start my day. It gets louder as I open up more stuff, use more tabs in firefox, edit in photoshop, etc. Well, my brothers dell recently died on him, and he got a new harddrive, bla bla bla, that was my chance to open my laptop and check around, I saw my fan was FULL of grey stuff, I guess you can call it dust? but this was more ground than dust, more like powder? So my brother had bought something to spray inside his laptop, he sprayed a little in my fan, cool, cleaned it a bit. Hair was still rapped around the blades though (I pull my hair a lot) hehe. So that seemed to quiet my fan down, but there it goes, running hard again. So that didn't really solve it, but on start up it sounded more quiet.

Now, that's my background info, here's what happened today. I was watching a video on youtube about water drops (I'm a photographer and was curious about how to take one, I knew how but I was wondering how to light it) and I set the movie to HD, my computer started to REALLY heat up, I checked the temp with a fan app I downloaded, and it was nearing in the 90s almost. Then after the video was done, it started to make a pretty loud sizzling noise, like when water boils over on the stove. I got really freaked out, turned my computer off, kept it off for a while to let it cool down. Then time went by, I took my feather duster out, (like I do often), to just clear the dust off my computer, around the speakers, keyboard, put a feather between the keys to get those pesky particles out, or at least I tried! Then I turn my computer on, odd, but now normal, it starts up quieter than it usually does. But now it acts different. It made a tiny sizzle noise here and there during start up, but was mostly quite like always, until I'd move my mouse. I then plugged my mouse in, and usually the fan starts going right about now and eventually I'd be able to hear it once I double click firefox really well. But nothing? My fan stays cool, and quiet. I then watch videos on youtube, have a lot of tabs open, have iTunes up and running. Still nothing, but nice quietness. But also at the same time, this is really abnormal. I've never heard it this quiet since the first day I got it. Right now it's more quiet than my Xbox, and usually it can get a lot louder than my Xbox.

So to sum it all up (I'm sorry if I wrote to much when it might not be a big deal) my fan is abnormally quiet, and usually it's revving up to almost in the 90s where I'd burn my self touching the fan area almost(this is when I'm running a lot of stuff though, most the time it's in the 80's, right now its in the 50s!!!!!!!!!!!!!!!). I'm curious if I could have damaged something? or maybe what ever was making it run hard, stopped making it run hard.

Does anyone have any input?!

-Amir (once again, sorry if this is too long, and I find it's not bad at all)

At this point, you'll probably have to take it apart to give it a good cleaning. Canned air would be a start, but you might need to manually pull out the hair or other big debris.

If concerned of temps and comfortable with the process,
Dismantle the heatsink(s), clean off old thermal compound, apply new thermal compound and re-attach heatsink(s).