# Noisy cpu fan on Dell Dimension 8400



## hodsocks (Aug 12, 2004)

I have been looking at a Dell Dimension 8400 which won't boot up, all that happens is the cpu fan/case fan spins up and just gets steadily faster until it is running flat out and making a hell of a noise. There is nothing on the screen and the 4 diagnostic lights at the back are all off and the front power light is orange. 
I blew out the heatsink and reseated the memory and the machine booted up but when I restarted it the same thing happened ie noisy fan, its obviously a hardware problem but as it won't boot into the BIOS I an restricted as to what I can do.

The problem is obviously a hardware problem as its not booting into the BIOS, so far I have tried the following:-
Removed the memory and reseated it, tried just one module in one slot then the other, swapped modules and slots.
Removed all cards, then put back in the graphics card.
Cleaned out the heatsink but don't think its heat related as it spins up in a matter of seconds.`
Reseated all cables and swapped for others, tried the SATA hard drive in a different mobo connection.
Cleared the cmos.
Tried new PSU, a normal psu works with this mobo as its a recent one, I think its only older Dell mobo's that had a proprietory psu. I checked the wiring in the 24 pin plug before I fired up the machine of course.

Whichever of the above I tried sometimes it would fire up OK but when I switched it off and then back on again I had the same problem with the noisy fan. I am begininng to wonder if it maybe a dodgy mobo or processor.

The Dell forums confirm that several people are having similar problems with this model and have fixed it in any of the above methods, there doesn't seem to be any one cause of failure.


Has anyone any experience of a similar problem or any suggestions where to go next cos I seem to have tried all the options I can think of.


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## gr00m (Oct 9, 2005)

I have a Dell 8400, though it's 8 years old, and the fan noise is the same with mine. It'll be really loud for the first 5-10 min, but then level off to a quieter mode, but still relatively loud in comparison to newer models.

As for the boot issue, you should search Dell's website to see what the 4 lights in the back mean. I had an issue with mine several years ago, called support and they were able to instantly diagnose the problem from the red/green light combination.

My personal opinion though is you have a short in the mobo (which is what happened to mine as well). From what you say, it's booted sometimes and not other, but only after some playing around with the hardware. Could be you bumped something into place when it booted and knocked it back out when it wouldn't.


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## Felicia101 (Jun 6, 2008)

I am new here, but I seem to be having a similar problem. My Dell Dimension 8400 was great for the first year but I have been having booting problems on and off for about a year now (which is really strange because it will run fine for months and then start again). I will try to start it and it makes a sound like an alarm clock and the fan will run very high. If I keep shutting it off and trying it again it will sometimes start (like now). On occasion it will try to start but will not boot and will freeze so I have to shut the power supply off and try again. I have run diagnostic tests on it when it has started to boot and the tests say nothing is wrong. In the past I restored the system to a previous date and that seemed to have helped. I just did it again and we will see. I opened up the computer (which I had never done before, I don't really know much about working on them) and I did notice it is a bit dusty so I am going to get some compressed air and try cleaning it. Have you had any success and does it sound like the same problem?


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## Bruiser80 (Jun 11, 2008)

I just talked to dell chat support today. They suggested I put a new fan in. I agree that it's most likely a loose connection on the mobo that posts the cpu temp as REALLY HOT. I actually have a second fan laying around on a Optiplex I'm putting together (it's working too ;-) ). I'm going ot swap them out and see what happens.

-bruiser80


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## Sootytd (Oct 16, 2009)

Has anyone checked their capacitors? Am having a very similar problem with fan, no boot & beeps but no colour indicator. Mobo capacitors are bloaded so think this is a contributing if not the problem.


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