Bad Ram Slot on Motherboard?

Hi, this is a follow up question from this one:

In my previous question i was worried that my Ram sticks where Bad, faulty, but i runned some tests on each Ram stick at once (separatedly), and they all came OK, with both Dell Diagnostics and MEMTEST 86+.  

The strange thing was the following:
I formatted my harddrive, and reinstalled XP Pro Sp3, after that i runned again MEMTEST 86+ with all 4 sticks inside, and all Tests where OK!
But with Dell Diagnostics, The tests only passes when ONLY ONE stick inside, if i put one more on the SECOND SLOT, All memmory tests have ERRORS (infinte number of errors!)

So my Questions are:

1) As someone else suggested (nobus) maybe is my motherboard, so How Can i Check if is actually my motherboard?? (All Dell Diagnostics tests on motherboard are OK).

2) If All memory tests on Dell Diagnostics throw errors, why do my Programs work (Ram demanding programs like Photoshop, Autodesk  Maya, Adobe After Effects....) ???

Thanks for your help

My Specs:
Dell Precision workstation 470 (3 1/2 years old PC)
XP Pro Sp3
1 Harddrive SATA  160 Gb (or 150 Gb) approximately
3GB Ram Total: (400-MHz DDR2 SDRAM)
      2 *  512Mb Ram Modules
      2 *  1Gb Ram Modules
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Generally you run a memory test as part of the process of diagnosing a problem with a PC.
You say the computer is working as it should except for the Dell memory test. I would stop running the memory test. If it's not broke, don't fix it.
you can always try to run from from a live cd, like Knoppix; this will show if your hardware has problems by not running .
The MemTest86+ program is one of the best for testing memory.  It is not 100% accurate; only a very expensive hardware RAM tester such as those used in factories  is that good, which means it is possible you could have bad RAM that passes the test.  In my experience, if it says you have bad RAM, then it is very likely you do have bad RAM, but if it passes, there is still a slight chance you have bad RAM.  You would then have to try different RAM that you are sure is good in this machine to rule out the motherboard.

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Check your BIOS and see if it permits manual adjustment of the memory speeds.  If it does try winding the memory down and retesting with the Dell utility.

Errors may go away if the memory is downclocked in my experience.
Hmm.  You may have asked the memory speed question in another thread so you can probably ignore my previous comment.
unrinoceronteAuthor Commented:
Hi, please excuse me for the taking so long to response, i have not beeing able to run more tests because of time, been incredibly busy, but i will run them today, and post and close question tonight.

unrinoceronteAuthor Commented:
!, i feel like a kid again! being reprimanded...anyways you are right Qlemo.

I apologize to the members that have kindly responded to me with their suggestions, and i will now close the question.

My conclusion tough was that the computer continues to throw RAM errors on the tests, but somehow it works OK.  And i dont want to buy new ram just yet, because i just ordered a new computer from Dell, so i will wait to have more money again to buy some more ram. In the meantime this computer will not be my principal computer anymore, so i will have more time to fix it.  Then i will post again, and i hope there a re no resentments, and you guys help me again.

thanks you all, and please excuse me that i abandoned the question (work was incredibly busy, as i posted in another question, i didnt even noticed that more than 20 days have past....!)


unrinoceronteAuthor Commented:
Thank you all!. Please excusme for closing so late.
unrinoceronteAuthor Commented:
@ Dbrunton: Yes, the computer is a DELL, so i can not do anything manually to the BIOS regarding Ram.. but thanks for your response.
no need for're welcome !
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