Adding more memory to W540 problematic

[a1s2d3f4]

I got a W540 machine recently (Win 8.1x64 ). It came prepackaged with 2 4GB Samsung memory chips. M471B5173EB0-YK0.

I used memtest86 to check that they were not faulty.

I then found and purchased a single 4GB module M471B5173DB0-YK0. I was hoping to have 12GB of RAM to play with.
(The only difference, as you can see, is the "D" - which refers to the date of manufacture of the module, but all other parameters are the same, of course.)

I used memtest86 to check that module alone to make sure it is not faulty.

I then put in all 3 modules into the slots and couldn't get the machine to go into POST: The Lenovo splash screen didn't come up. The booting process just stopped with a blank screen.

I then used the new module only in one of the top slots to boot the machine - OK.
I used the new module WITH one other old module - so just two modules in the top slots - OK.

I searched online and found various forums where people would complain about a similar issue with W540 memory upgrade - but no apparent solutions.

Can anyone explain this problem to me?
Will this be fixed if I buy yet another 4GB module to max out all 4 slots, or is there something wrong with my motherboard/bios/something else?
Does anyone know?
What other information would it be useful to provide here?

Thanks.

[a1s2d3f4]

I just managed to seemingly solve this problem.

Firstly, I did upgrade to the very latest BIOS (2.17), though I don't know if it matters here.


What I did with the memory modules is the following:

The originally-installed modules were in the top slots (closest to the module cover).
I moved them to the bottom slots and installed the 3rd (new) module into the top slot closest to the battery.

It seemed to take a little longer to start at the beginning of the POST, but it booted just fine and the system reports 12GB for me.

Thanks for reading.