Dell PowerEdge T110 Server with 16 GB of RAM only has 8 being recognized by BIOS and OS

Hi all,

This is starting to drive me nuts. I just recently upgraded my Dell PowerEdge T110 server from 4 GB (I bought him with 4 GB back in 2011), up to 16, though I began with 8, and the saga just goes downhill from there. The issue is that only 8 gigs are recognized in BIOS, and in Windows as well. According to a Crucial scan, his two mid slots are empty.

I have all four slots filled with Crucial ECC PC3-8300 modules, compatible with this model according to the site (tried to get modules from Dell themselves, but was told by a salesman that they didn't have any more). I tried the following configurations to ensure that I wasn't seating the modules incorrectly: two Dell modules on the two outer slots (the machine will boot in that configuration as long as no middle slots are filled).

Two crucials with no Dells: (machine will not boot and flashes his red light on his front panel)

Two Crucials (Crucials on the edges) and two Dells (Dells in the mid slots): Machine will boot,, but only recognizes 6 of a total of 12 gigabytes in that case

Crucials filling all four slots: (He'll boot, but only recognizes 8 of a possible 16 GB.

In all cases, except for the case of the Dell memory-only configuration, I get the message at a certain point: "strike F1 to retry boot", and when I do that, he continues his boot process as if nothing happened. I can work with that, though it is a pain in the buttt considering this machine is running a Hyper-V role, and I really don't want to have to babysit the unit in order to ensure that it starts up again after Windows update, for instance. His two mid slots were empty since I got him, and it seems that filling them hasn't done anything to make the BIOS recognize that anything is in the slots. Wwhat the heck am I missing? I've not been able to run diagnostics yet since I don't unfortunately have a set of eyes wwho can understand Dells error codes on hand at the moment. My APlus and NetworkPlus certified friend tells me that this points to a motherboard issue. It looks like it, but how could those middle slots jut have "gone bad"? Doesn't make sense.