I added 2 ram modules to my D10-6427, now the Ram settings are 6x2GB and 2x2GB setting as mainboard diagram. All seemed well and performance seems to be a little higher.
Following this upgrade, I was surprised after opening the task administrator and seeing only 4 CPU graphs like 1 Xeon working, but the performance seems to be the same or very similar. I have tested some apps, Lenovo ThinkVantage, PC Properties and BIOS only shows 1 CPU.
I removed the modules added to test and reboot, the D10 showed a running setup message with the Logo screen and I could not start windows 7, or enter the BIOS with or without new RAM modules.
During boot up, when displaying hardware devices, the SAS HDD aren´t shown, only DVD and SSD.
I have tried to start with a BIOS CD, but the CD doesn´t start.
The D10 boots, Logo screen, hardware devices, show PXE ctrl+s, and Logo screen again.
To debug following memory changes that led to unexpected resuslts, try to install one FB-DIMM in slot 0 (refer to the chart on the access panel), reset the BIOS using the jumper (instructions), and see if that helps. Operate the system on just one memory module during testing to help eliminate variables.
If following these steps, you still don't see the second CPU then you'll want to remove both CPUs and install each individually in socket 0 (labeled "CPU0" on the planar) to test for failure. This will determine if one of the CPUs coindentally failed, or if both work and the issue is tied to BIOS or the previous memory upgrade. Be sure to have a good thermal compound on hand. shin-etsu X23-7783D is an excellent choice here. If one of the CPUs has failed then contact lenovo support if your system is under warranty.
If both CPUs are found to work properly in CPU0 socket 0 with a single memory dimm, then:
Restart Windows and open "msconfig" and without changing anything, close the windows with "Accept" button, and allow system to reboot. After reboot, Windows should start normally and display 2 Xeon and 8 cores, PC properties and Task Admin, Everest and CPUz shows 2 CPUs too.
Reinstall the memory and check that all modules are correct speed.