terrible CPU or CPU fan noise on some startups - BIOS alteration?

I have got a custom built machine: Asus M2N68-AM SE2 motherboard with
an AMD Athlon I X2 250 3 ghz CPU, plus 320 hd drive, 4 gb RAM
(Buffalo, PC6400, a compatible speed with the m/b), PNY Nvidia G210
card, running Windows 7 64 bit.

I had some instability problems when I'd had some apparently faulty
Elixir RAM - blue screens, and warped thing shappening on the
display. For a little while, waiting for the Elixir to be replaced by
a second stick of Buffalo RAM - asked for by me because the other one
seems fine - I only had 3gb, adding a 1gb generic stick that came with
the machine. Today is the first time the CPU has made this terrible
grinding din. It stopped doing this after I shut down and started
again.

Could this be simply because my home is unheated? February in England
and no central heating, which I can't rectify without trebling my
electricity bill. My laptop and netbook and other appliances cope and
have for fifteen years here. I would prefer to ignore this factor if
anything else is also possible, simply because this factor is
unresolvable.

Or, can you advise me about any Bios or Windows settings that might
need changing? I've got Windows' power setting set to High
Performance, and to not go into sleep or hibernation mode. Is this
tied in with ACPI and all that, i.e should anything be altered in the
BIOS pertaining to that?

My BIOS has sections for both Q-fan and Cool 'n' Quiet, but both these
things seem to do the same job, which I'm a bit muddled about, and the
little manual hasn't been enlightening. I had Q-fan enabled for a
while, and then I disabled it as it didnt seem to do anything. Now I
have Cool 'n' Quiet enabled.

Have I forgotten anything? This is the first time I've gone 64 bit -
does this require any BIOS or other changes?

Modest as the cost may seem to some I really can't afford to have this
machine die on me.

I will admit that I have one 'cracked' bit of video-editing software
running, and I'm happy to admit this because I fully intend to buy it
in a month's time as it is not as expensive as I'd thought, £35, and
needed to run it fully to know it suits me. But though scans with
Avast and Defender show no viruses, it did occur to me that might not
be foolproof. But I would think Keygen is famous enough that anything
bad smuggled into a version of it would soon be found.

I'm dreading having ot talk to the company I bought the machine from
because it would be so long-winded and they'd probably try to get out
of responsibility some way or another if there is a fault with the CPU
or motherboard. Memtest has okayed the RAM, anyway. The CPU
temperature checks out as normal in the BIOS too. The PNY card has a
little fan. The case has a fan which I was told wasn't necessary to
connect - it was very noisy so I've not bothered. With a case side
off I put my hand near and all seems cool and very, er, 'fanned up'.
I've had the machine a month-ish. It turned out that one connector
was on wrong as set up by the company, a connector that makes the HD
activity light work - I'm not too inspired by the thought that I as a
nervous novice have put this right after bottling out of fully
assembling it myself from the components.

Or maybe Windows 7 64 bit isn't stable?

All advice, as jargon-free as possible, would be appreciated. Many
thanks in advance.