This is really intriguing. The PC has been perational for only 2 years.
Would flashing the BIOS help?

On 14/08/2010, John Sproule <[log in to unmask]> wrote:
>
> If this is the original fan, and there is no chance that it has been
> disconnected and then reconnected to the wrong fan header, and it is
> spinning normally, this is unusual that the motherboard would tell you that
> no CPU fan was detected.  Other than the motherboard being defective, the
> only other option I can think of is that sometimes an older fan may not spin
> up to its normal speed very quickly and the motherboard may fail to detect a
> running fan during the initial boot and therefore conclude that there is no
> fan connected.  I would think that you would be able to see that the fan is
> having trouble spinning up, when the computer is first started, if this was
> the case, however.
>
> I take it that either the BIOS does not have a hardware monitoring section
> or the computer shuts down too quickly for you to have a chance to see what
> the motherboard's monitoring function might have to say about the CPU fan's
> rpm/speed.
>
> John Sproule
>
>
> Date:    Fri, 13 Aug 2010 16:59:09 +0300
> From:    Romario chipo <[log in to unmask]>
> Subject: Re: Fan cannot be detected
>
> The fan has not been replaced before. The fan came with the machine
> and it spins quite okay thats why I am amazed by this error message.
>
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         PCBUILD maintains hundreds of useful files for download
                     visit our download web page at:
                  http://freepctech.com/downloads.shtml