HP DC5850 run away CPU fan

I have a Hewlett-Packard HP Compaq dc5850 Micro tower PC, now running windows 7 pro 64-bit. That was new in late 2008. Originally it came with vista 32-bit downgrade able to XP pro 32 bit, running on 2G RAM, and 160G C drive with a 2.30 gigahertz AMD Phenom 8600B Triple-Core processor. It also has ATI 3100 integrated graphics as well as integrated NIC at 1G and integrated High def audio. In the first few months I had the system, I upgraded memory by 4G and total Disc space by 500G by adding a D drive; then upgraded to windows 7 pro 64-bit.

Overall, I have had a good experience with the PC but it has had problems while in its 3-year warranty. I did need to replace the C drive and later it original RAM devices. Yes HP did these replacements and swaps, under warranty; that meant I had 6G memory for a long time before the HP 2Gig failed out of warranty, leaving me with 4Gig now. Yes I have always had the Unit on an UPS; I even replaced the old UPS with a more powerful unit in late 2009 or early 2010 when the old UPS showed signs of failure. Now instead of serial based UPS connection it is USB.

Over the last few months I have been getting blue-screen errors of all sorts. Ranging from video related errors, Memory faults, Disc read/write failures and processor flag errors too. After numerous repair disc runs or re-install of windows, the disc read write errors wore corrected by the HP drive sanitation utility disc repair/wipe after failing the extended test. The non video ram was tested by a bootable CD of memtest86 v4 running extended test as well as MS memory Diagnostic. Both run multiple times, both passed multiple times. I was able to find a CD based video diagnostic for ATI and the Video passed repeated stress test as well. Over Labor Day I conducted these test and re-installed windows 64-bit; on the following Monday windows informed me I needed to activate windows, so I verified the correct key and called to do so, successfully.

With that background given here is the question. Recently over the last two or three months, for no apparent reason, mainly on boot the fan races to top speed and the system shuts down to protect itself. I researched this a little and found one cause to be inadequate airflow over the CPU to keep it cool; the recommendation made sense to vacuum with a computer vacuum and be sure airflow is not somehow obstructed. I followed the recommendation and the blue screen errors returned. I am now thinking all these problems are related to the CPU temp sensor. Is it on the CPU fan or the motherboard, and can raising the fan speed in BIOS help prevent the problem, particularly if it on the motherboard. please advise because I have heard from others in charge of 5850 and 5750 systems run away CPU fans are now more common in 2008 vintage units.
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  1. Best answer
    Go to HP website do search on dc5850 look for technical referance guide. Look on page 4-12 to see if this might be of help.
  2. Thanks, found Tech ref guide for DC5850 series and found refs to temp sensor and 'thermal' starting on page 41 to 81. increasing min fan speed could work but if sensor is bad a new system board is needed. could it be as simple as removing CPU fan, cleaning fan and CPU (with anti static precautions of course) and replacing thermal gel.
  3. Best answer selected by jmgrayii.
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