computer has noisy fan

Today I walk into work and the computer is making a noisy sound coming from the back ,so I decide to give myself a challenge and try to resolve it.
The first step is to look at the power supply fan at the back of the box and make sure its spinning if it is then the problem may lye elsewhere if it´s not spinning then we will have to replace the whole power supply unless you´re not afraid of opening a power supply and replacing that specific fan and also risking to get a shock ,if the power supply fan is working then we will have to open the box.
I open the box side panel by removing the two screws at the back holding it.
I then remove the panel and while the computer is on I have a look inside, since I only have two fans( one on the power supply and one on the CPU) It has to be the CPU fan that's at fault and it sure is since its not spinning correctly.
To remove the CPU fan the computer must be switched off and disconnected from the mains power .The best way to do this is to lye the box flat on the its back so you can work easier also touch the chassis of the box(the metallic structure of the box) to ground yourself before touching any parts.

Now we have two options to repair the fan before we go further .
1: we replace the Heat-sink and fan
2: we add lubricant oil to the ball bearing of the fan

I recommend the first option since oiling the ball bearing can be messy and the problem could repeat itself quite soon.
To remove a Pentium 4 CPU in the socket 478 form factor ;http://www.intel.com/support/processors/pentium4/sb/CS-007989.htm
For the newer Pentium 4 CPU socket 775 ;http://www.intel.com/cd/channel/reseller/asmo-na/eng/products/desktop/processor/processors/pentium-4/tech/99345.htm
For AMD CPU you basically lift the metal clip with a flat screwdriver downwards towards the board then move it forward then up;http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_869_4348%5E6678,00.html

After removing it you should go buy a new one and no more noise.
I was lucky to have a used one that was still noise free, you should actually buy the Fan before you remove the Fan from the board unless you need to take it to a computer shop and ask for a similar one.