Dell OptiPlex 755 memory error.

Have you considered that it might be one of the dimm sockets and not the ram at all. Try removing 1 module and see if the error code remains. If so try the remaining sockets. This should enable you to find out if its the MB or not. Good Luck.

Take it one step further ... boot to the 32-bit diagnostics to test the memory with MPMemory.  This will tell you which DIMM, then you can swap positions to see if it follows the memory or stays with the slot.

Take it one step further ... boot to the 32-bit diagnostics to test the memory with MPMemory.  This will tell you which DIMM, then you can swap positions to see if it follows the memory or stays with the slot.

I have already run the internal memory diagnostics as well as the full 32-bit diagnostics including MPMemory.  There is never a problem detected only the issue where the disk test queries the empty DVD drive and mistakenly suggests a potentially failing drive.  In an earlier reply, I incorrectly stated the speed rating of the memory modules as 533MHz, the actually speed of each is 667MHz.

When the 3 4 error occurs the system never completes POST to allow booting to the diagnostic media.  So, I can only run the diagnostics after I have cleared the fault in this case by reseating the memory modules.  Once inside the diagnostics no real problem is ever detected.

I’ve considered this problem as being a capacitor issue as I have experienced so many times in the past with the older OptiPlex GX models.  In this case, that doesn’t appear to be the reason the system halts at this specific point.  Once booted, the system appears to function normally.

I would agree with you that it is not the memory but the board itself.  I have also seen PCI cards cause what seemed to be memory or processor errors ... as a long-shot final follow-up ... do you have any PCI cards in the system?

Nothing in the adapter slots.  It's a basic system in a desktop style case.

Yes, the actual problem must lie within the system board itself.  While searching for a solution online, I found what seems like an almost endless number of support queries involving the Dell OptiPlex 755.  Given the volume of technical complaints it’s somewhat obvious this particular model suffers from extremely poor design and engineering.  Almost all of our 755’s experience this exact same trouble, some much more often than others, with the worst case being weekly POST failures requiring the temporary fix of reseating the system’s memory modules.  Many others of this same model also experience network connection and multicast failure issues which until now I had not connected to faulty system hardware.

At this point, it seems our only option is to have the system boards of all of our OptiPlex 755 machines replaced under warranty.

Hi John

Did you get this resolved - was it a warranty job?
I have a 755 sff that now only manages to complete about 1 post in 20, and then doesn't stay working for more than 10 minutes!
A real shame, it's been faultless for 9 months running with core2quad, 8gb RAM as an ESXi test rig at home. Just the last week it went flakey with regular reboots several times a day, now the 3+4 LED issue with no post :(

That's just how computers work.  As small-scale as they are and as finely-tuned as they are, one minute they will work fine, then after the moment something happens, it doesn't work.  Heat, electricity, dust, vibration, etc. in the smallest amounts can cause damage in split milliseconds - works one minute, not the next.  Run the diagnostics, swapping DIMM's to isolate which is the problem, then call it in for a replacement.  I'm assuming this is still under warranty since it is only 9 months old - if not, memory is not expensive to replace.

While rebuilding a 780 mt I got the same error code and after a little looking around I found the CPU to be bad, after installing a new core 2 dual the error cleared and all was well.