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Well you did find out where the noise is coming from after trial and error. You've detected it coming from the PSU [power supply unit]. If the device below fits the description than it is so.
As you are finding out computers need a lot of care in order to operate smoothly. Any computer can DIE out of the blue to a user who does nothing but use their pc everyday without maintaining it. They're a lot like kids, plants, pets, etc. I'll give you a few tips on how you can maintain your pc physically, but first let's take a stab at your PSU issue.
Most PSU's build up a lot of access dust on the fan and the inside grate grill. Sometimes the PSU will also get dust stuck between the fan and the bearings [the copper wires spun up into a ball right behind the fan which is hard to see]. If there is any dust buildup at the bearing area it should come out naturally on it's own since you already cleaned the fan. But one thing you probably forgot to do was to blow the dust inside the PSU through the grate/grill panel. That way you blow the dust outwards and it will shoot out of the fan at the back. You need to use a can of compressed air which you can purchase at any local small/major computer store for about £2. Here's what a can of compressed air looks like below.
Buy one and blow the dust out of the entire inside of your pc and the inside of your PSU. As I mentioned before clean the PSU from inside out when you blow it with a can of compressed air.
Than take a moist [not wet] q tip and clean the fan, and after your done turn the q tip around to dry the fan. Lastly turn on your pc and you may or may not hear the buzz again. If you do aim your mouth right over the back PSU fan as if you were trying to look into the fan from the top. Keep your mouth a good 5-6 inches away from the top of the fan and blow inwards with your mouth in 3 second bursts of strong yet gentle breaths of air from your lungs. Use your hand to cup the air coming out of your mouth so it goes inwards if you have to. But don't cover the entire darn PSU fan with your hand because it's supposed to blow air out while your blowing in from the top. Do this for 1 minute than stop... The noise may go away while your doing it, or a couple minutes after you stop. This method is used to try and get any dust buildup out of the bearings which is a hard place to reach.
The picture below is not an actual bearing behind a PSU fan but instead a coil of copper wire which is practically the same thing if you use your imagination. If your lucky enough you'll see it behind the fan or any other pc fan for that matter. You may need a flashlight to see it though.
Anyways if your PSU is still buzzing and humming 1-3 days after you do all of this important cleaning you may be in for a deadly ride. It can mean that the dust has built up so much that it has damaged your PSU to the point of no return since you've never cleaned it or your pc either. Your supposed to blow your entire pc with a can of compressed air every 1-3 months. People think dust doesn't build up in a pc when it really does A LOT. & if the dust is thick enough it can create moisture from the heated pc components which can fry the hardware inside, or obstruction of airflow to fans. Like I said if you do the cleaning process I've mentioned and the noise persists for over 1-3 days your PSU may be dying, and if it does it can kill the entire computer when it goes and you'll need a lot of pounds to buy yourself a new pc! & that's a lot of weight! LOL
So if you still hear the buzzing from your PSU 1-3 days after this cleaning procedure you'll have to buy a new PSU from your local small/major pc store as this is the only way to save your pc and bring it back to normal life before your PSU dies and kills the pc with it. They can range from £10 and up, but be sure to check and see if the main fat wire plug from your PSU is a 20 pin or 24 pin plug [it's the hugest plug that comes from your PSU and attaches to your motherboard]. You have to buy the same 20 or 24 pin plug PSU or it will not attach to your motherboard to give it power. If you do have to buy a new PSU in a few days after your cleaning procedure, I'd say take a few pics of the way the PSU wires are connected to your internal pc parts so you can buy a new PSU and connect it the same way. Installing a new PSU is so simple, probably the easiest pc install there is [takes about 5/10 minutes to install]. You can search google for help if you ever get stuck on doing so, but it's way too simple so I don't think you'd have to. Also make sure that you buy a PSU that is the same wattage or more than your current PSU [you can find the watt rating on the sticker of your PSU - for example my PSU is 450 watts of power - another example is to look at the first picture in my post where it shows a PSU sticker]. Buy the same wattage or get one that's higher if you want to, it really won't matter as long as you get the same or more. & that's all you need to know about getting a new PSU!
As I mentioned your entire pc can die meaning everything can be fried and killed inside if your PSU decides to blow itself away. I've seen it happen many times. I had a mutual friend who brought me his pc to fix a while ago. He never cleaned the entire inside of his pc regularly. The pc was practically asking to malfunction and ruin. I took one look at it and told him it was over and there was nothing I could do. The PSU in his pc decided it was time to say bye bye and when it did it killed his hard drive, ram, motherboard, sound card, video card, etc. It took everything and he lost years worth of data on his HDD [hard disc drive].
Here's some tips on how to clean your pc:http://www.directron.com/cleaning.htmlhttp://reviews.cnet....-6240575-1.html
Remember to always make sure your pc is off and unplugged while you service it so you don't kill yourself by any electrical shock/surge/etc. And always touch the inside metal case of your pc with your hands before touching anything inside so it will release any static electricity you may have on your body. If you touch the inside of your pc without doing so you may shock your pc components with any natural static electricity buildup on your hand and that can kill/damage your pc components. Try to service your pc on top of a wooden table or any table. & stay away from servicing your pc while standing on a CARPET!
GOOD LUCK AND BE SURE TO LET US KNOW HOW EVERYTHING WENT.
Edited by superstar, 26 March 2008 - 10:00 AM.