Your modules are actually DDR2-667 according to JEDEC standards, DDR2-800 achieved by overvoltage in signal lanes from standard 1,8V to 1,85V or even 1,9V. So due the time memory controller inside MB chipset slightly degraded and become uncapable to work with four DIMM filled. Reduce memory speed & voltage to 667/1.8V in BIOS and try with four DIMM again. If work, this is your config till the end of PC life.
I tried the setting change and nothing changed. The computer had previously worked with all four memory slots filled. It just started giving the three beeps memory error after being turned off for a couple of days.
More information: I just noticed that with two DIMMS in the black slots, the computer only sees one. It reports that only one slot is filled. However the computer boots with no error message.
I ran a D975XBX2 for a few years. I think it only officially supports 8GB total memory. From your original post, it looks like you are trying to install 16GB.
I'd suggest that you download the "Technical product specification" from http://www.intel.com/p/en_US/support/highlights/dsktpboards/d975xbx2 and compare your configuration against the permitted memory configurations.
From the "Technical product specification" document
1.4 System Memory
The board has four DIMM sockets and supports the following memory features:
• 1.8 V and 1.9 V DDR2 SDRAM DIMMs
• Unbuffered, single-sided or double-sided DIMMs with the following restriction:
Double-sided DIMMS with x16 organization are not supported.
• 8 GB maximum total system memory. Refer to Section 2.1.1 on page 49 for
information on the total amount of addressable memory.
• Minimum total system memory: 128 MB
• ECC DIMMs and non-ECC DIMMs
• Serial Presence Detect
• DDR2 800, DDR2 667, and DDR2 533 MHz SDRAM DIMMs
Sorry for the confusion, I have four 2GB DIMMS, Kingston KHX6400D2K2/4G
Capacity4GB (2 x 2GB)
- Speed DDR2 800 (PC2 6400) (16 128x8 SDRAM)
- Cas Latency 5
- Timing 5-5-5-15
- Voltage 1.85V
- Heat Spreader Yes
- I also have four Kingston 2GB DIMMS
That I have also tried with the same results.
They are: 1.8V with 128x8 SDRAMS
I have had both sets installed at different times in the computer working fine and showing 8GB.
Here is an update - after looking at the documentation.
If I install memory in Slot 0 of Channel A and B (blue connectors) I have no problems and can get 4GB to show.
If I install memory in any Slot 1 Channel A or B or Both (black connectors) I get three beeps on boot.
I have swapped the memory DIMMS to the blue connectors and verified that all four will boot without issues in the blue connectors. So it is clear that the memory is not the issue.
It would appear that there is a problem with the motherboard.
I'm guessing that there is no repair program for boards this old.
I'm rather dissapointed as of all the computers I have ever owned, this is the first that has had a bad motherboard.