I have Lenovo M91P 7052-b5u i5-2400 (spec sheet) with 2+1 GB RAM

look like this.

Because I have 4 sockets, I decided to add 2 more.

Yesterday I added Kingston 4+2 GB RAM 99u5471, but the PC didn't boot. It was black screen - no POST.

I thought maybe the new RAM wasn't compatible - but after I took out the old 2+1 RAM, everything worked just fine.

So right now the PC boot only if I putting OR only the old RAM OR only the new RAM but not both of them.

What can cause this? Is it because the size is different? (the Kingston is smaller than the old ones)

(I already tried to switch between the sockets)


  • My best guess is a difference in speed between different types of RAM chips. Getting the same make/model for all chips may fix this. (Yes, that might mean replacing some working equipment in order to get some more-compatible equipment.) – TOOGAM Jan 21 at 12:41

Sometimes ram is required to be upgraded in pairs with the same size and spec. Use the Crucial Ram Scanner which will tell you what ram you need and if it needs to be upgraded in pairs or not


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Try resetting BIOS battery before adding new rams, then check new rams one by one to see which works. when you dealing with RAMs, sometimes PC doesn't boot, because it need BIOS reset. even if rams are working good. also different types of memories doesn't work together at some cases. they must be similar to work correctly...

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  • Tried.. didn't work... Why different types are causing trouble..? – Dvir Naim Jan 22 '17 at 10:20
  • Even if specs are same but because they are from different manufacturers that may cause compatibility problems... Some different RAMs works together, some not. I think that's the case – George G. Jan 22 '17 at 10:33
  • there is nothing to do ha..? Out of curiosity - does the size says something about the performance? – Dvir Naim Jan 22 '17 at 11:11

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