Dell Dimension 4700 Will Not Start - B Diagnostic Light is Amber, others Green

Dell Dimension 4700 Will not boot.  Fan is constantly blowing hard, but no other activity is seen.  The B diagnostic light is amber and ACD are green.  No video or HD activity.  No Beeps.  No other accessories plugged in.  Removed memory and HD to no avail.  Please no guesses here - I cannot just throw new parts at this thing in hopes it works again.

Thanks.
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slsmithAsked:
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cedarghostCommented:
With the memory removed, when the computer posts,  the computer will give several beeps.
You have power because the fans spin and you have lights. If the CPU is bad you should get high/low beeps. If you have the memory out and it isn't beeping you have a bad motherboard.  If it was your CPU you would get  an error code beeping.
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BillDLCommented:
How many memory sticks do you have fitted, and is this something that just happened?

To save any others from hunting for the diagnostics light info:
http://www.webmadeeasy.net/ComputerDocs/Dell/Dimension/4700/ServiceManual/adtshoot.htm#wp1054305

I don't see a permutation that matches your lights.  It's flagging up the Memory light (B), but not telling you why it's yellow, eg. D would tell you it's configuration issues.

Very puzzling, I'm thinking about this one.
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slsmithAuthor Commented:
With the Memory out (2x256mb), I power on the system with same result.  NO BEEPS, B DIAG light Amber, the rest are green.  Fans is constantly blowing hard.
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slsmithAuthor Commented:
Of course the system is 39 days out of warranty so that is not an option.
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BillDLCommented:
Strangely enough I was just about to go along with cedarghost's bad news suggestion about motherboard problems, and that was also the general consensus from the (apparently) expert suggestions here:
http://www.geekstogo.com/forum/Dell-4700-wont-boot-post-t183103.html

.... that was until I found this garbled and long post where some (apparently) not-so-expert people had a stab at guessing the problem.  The diagnostic lights were the same configuration as yours, however the Dell tech decided to change the processor fan!  From what I could see B = Memory, but then again your lights don't match any in the manual.

The problem seemingly turned out to be ... well, it's hard to know because it was stripped and rebuilt:

>>> "I had a bad PCI network card. The dell technician put in the new processor and then I had the same problem with the fan. He removed everything and began adding stuff back in piece by piece". <<<
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willcompCommented:
Disconnect/remove everything not needed for a basic boot. You should be left with mobo, CPU, PSU, RAM, video card (if not integrated), keyboard, and monitor. If it still won't boot, you have at least narrowed it down some. Swap memory modules and any other components you have available starting with PSU.

By swapping memory and PSU, you can narrow [roblem down to motherboard or CPU.

As BILLDL noted, the B diagnostic LED is associated with memory. There should be a second amber LED though. Absence of beeps is also unusual.
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willcompCommented:
CPU fan? There isn't one per se. There's a 9cm rear mounted fan. PC should boot and run with fan disconnected. Don't run for long unless shroud is removed and case is open.
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slsmithAuthor Commented:
I reseated CPU - no luck.
Removed fan - no luck
Cleared cmos - no luck

I think we all have it narrowed down to MB or CPU, but I am not interested in getting both  if it is only one of them.  Besides putting a known good unit in, what else could I do to narrow down the problem?  The MB was replaced under dell warranty about a year ago.

Thanks
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cedarghostCommented:
If it was your CPU you would get  an error code beeping.
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slsmithAuthor Commented:
OK.  So it is the motherboard, right?
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willcompCommented:
You usually do not get beeps when a CPU fails -- at least in my experience. Since you do get a partial POST and an unusual diagnostic code, I'd suspect motherboard is the problem.
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slsmithAuthor Commented:
Thank you all for your help.
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cedarghostCommented:
Yes. The motherboard, and you SHOULD get high or low beeps with this model Dell if you have the memory removed and the CPU was bad.  No willcomp, this is not the norm, but it is for this PC.
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BillDLCommented:
Thank you slsmith.
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