I have a Precision M4700 which has been working fine with 2 x 8gb PC3 12800 (Dell SNP8H68RC/8G).

Just added 2 more of the same memory units into the additional memory slots under the keyboard (to bring it up to 32gb) and it won't boot.  Powers on, but no fan and screen black.

It's a core i7 quad core and there was no sticker in the additional memory bay stating that the slots should not be used.  When running at 16gb the BIOS reports slots C and D as available but empty.

Tried loading the BIOS back to defaults and running diagnostics (at 16gb) but makes no difference.  I have tested the two new memory units in the primary slots and they work fine.

Any ideas?  Is the motherboard faulty?

Mark.