Poweredge R510 no longer boots after memory upgrade

[arontoms]

I have tried to upgrade the memory of a Dell Poweredge R510 from 4Gb to 8Gb.

Originaly there where 2 x 2Gb PC3 8500 modules seated in slots 2 & 3. So we purchased an additional 2 x 2Gb PC3 8500 modules from Crucial.

The problem is when we insert the new modules along with the old modules the system doesn't boot. We get the usual scenario where the fans, hard drive's etc spin but the monitor doesn't come on and the system doesn't boot.

I have played around with a few configurations:

1. New memory on its own in slots 1&2 - Result works fine 4Gb
2. New memory in slots 3&4 old memory in slots 1&2 - Result no boot
3. New memory in slots 1&2 old memory in slots 3&4 - Result no boot
4. New memory in slots 1&3 old memory in slots 2&4 - Result no boot

I have also tried to put one pair in slots 1&2 in the first bank and the other pair in slots 1&2 of the second bank - Result boots ok, however only recognises 4Gb (so confirming that the memory controller is on the CPU and as we only have a single CPU the second bank has no controller).

If anyone has any ideas about what the memory configuration should be, or if there is something missing I would appreciate your feedback.