Let's see if we can get a few more details from you that can help.
Memory model numbers?
Let's also not forget that the memory controller is now in the CPU on the 55 series chipsets / CPU's.
Check your CPU socket for bent pins as the interface is directly from the DIMM sockets to the CPU socket. 1 bent pin ...?
OZ2 PC3 10666 PN QCZ3G1333LV8GK
2.8 Gh i7 860 CPU
You seem to be "passing the buck" and blaming the CPU now? I have built severl computers and this is my first (and last!) Intel board- I have NEVER had a memory slot problem with any other brand of MoBo.
If you re-read my post, you'll see that all four slots work (but in different combinations) The notes about the latest BIOS update says nothing about solving this memory slot problem, which several people have reported for this same MoBo. So, I ignored trying to upgrade the BIOS.
So, how do I tell the CPU to let me use all four memory slots at one time?
Update the BIOS.
I use a lot of DP55WB's and certain single sided Crucial 2GB modules refuse to work in pairs (3 Beeps) until the BIOS is updated (with only one stick installed in Channel A DIMM 0). The BIOS release notes for the DP55WB don't really hint at that issue, but the issue is resolved nonetheless. I'm aware you have a different board, but it's worth a shot.
Any that complete POST.
In order of probability.
1) Bent CPU socket pin - Since the memory controller is in the CPU, one slightly bent pin will disable a DIMM socket.
2) BIOS - The Memory Reference Code that controls the functionality of the processor / memory resides in teh BIOS
3) DIMMs - Check the requirements, population and stacking rules. Single, dual or quad rank dimms all behave differently
4) Mother Board - Check the slots of debree and wipe DIMM contacts with rubbing alcohol. The board has a CPU socket, wires to the DIMM sockets and the DIMM sockets Not really a lot here that can fail or be bad..
5) CPU. - The CPU is soooo tested, it would be very strange to have an issue like you describe.
Sorry Gize- I was wrong- slot 2 ( Ch A Dimm 0) DOES work- it was the first slot I tested alone.
Doc- thank you for the logical rundown of possibilities. Since it will be such a "pain" to do, I'll try the Bios upgrade before checking for a bent pin, hoping that the solution lies in the BIOS upgrade. I will do that this evening and report.